EWP in Heroquest means more to me than a pile of cards!
I am a Game Mechanic. If games had a combustion engine, i would always be covered in oil up to my shoulders. Hacking games is actually more fun for me than playing them. If game companies would pay decently, i would never work in aerospace and also not in data science, both not. (whereas, the latter you can beautifully apply to games

)
I made an Final Liberation/Epic40k hack that is actually balanced even if the AI is stupid as bread. I invented a entirely new trading system for "The Settlers" because the current system was annoying me. I really intensively played Space Crusade, but nevertheless, the time invested in "correcting" the game was longer than the total playtime of my entire youth. I hacked 40k in the 6th and 7th edition so that it was actually fun to play 40k despite the special rule flood, and our club took over my ideas. The Kill Team rules of 40k, 4th edition, i made them available to Space Crusade because they are actually a lot of fun, sneaking around the board, trying not to be catched by the evildoer.
What is special about Heroquest for me is the EWP mechanic: You actually are asked by the rules to think of missions yourself. For me, a "Heroquest quest" is:
- Best case, at least one Game mechanic in the quest notes that you have never seen before
- a Mission difficulty/balancing that shall be achievable but challenging (Questimator 14 or 15 was proving itself)
- maybe one new monster (painted!

)
- a Warhammer map position of the quest that you can use in a greater, narrative context
- A small short story cut down to 5-10 sentences that gives the narrative players a bit of feeling, enhanced by matching quest notes
So for me the game begins before the game. I make a mission, i make the rules, i make a story. Afterwards it is quite rewarding for me to watch the players how well or not well they do with the mission that i invented, seeing where they have fun and where it was not-so-good so that i can be better next time.
Once you have prepared all that, you can compile it into a set of Cards with some Monster AI rules, true.

Zombicide and Conan both are missing the narrative part. Zombicide is a great game, i like to play it from time to time, and it is difficult, too. But it's missing the "something you have never seen before" part as well as the narrative and the "new Monster" part. The short story, you can put it in the bin. So what is good is the game mechanic only.
Conan is super-balanced between Overlord and Players. After? Beautiful models, but then nothing. It's a really really good skirmish. Not more, not less.
That said, back to topic:This thread is about how to use the beautiful Zombicide Black Plague or Conan Boards in a game of Heroquest.
Those Boards are really great. What i would like to do in this thread, is developing a method that allows a fellow Heroquest player to use those beautiful game boards in a game of Heroquest.
There are a few things that need to be done.
1) Defining several models in one field. Knightkrawler did deliver a nice definition that can possibly be reused.
2) Reducing the movement so that it fits with the new field size.
3) re-defining ranges. I have adjacent. Diagonal. Long/Extended (It is like diagonal, but in a straight line it has 2 fields range). Ranged (which is line of sight blocked by Monster), the same room (example is trap search), ranged magic (basically ranged, but ignoring monsters for the line of sight). And i have Anywhere on the board (for the Djinn or Fire of Wrath)
4) Find out how traps could possibly work if they cover only a small part of any given field
What i think we could do easily is that
1) Several models in a field: If it fits, it fits. If it does not fit, you cannot stay there. No-one is able to block your movement except if they attack you. (or everybody can stop you so that you have to stay?) If a field is completely full then adjacent attacks from neighbour fields can affect this field.
2) Movement reduction: Roll your dice. You can move one field if the result is less than 10, two fields if it is 10 or more. You get one additional field if you use your action for running or if your model has a special speed rule for moving.
Monsters with less or equal than 6 fields can move 1 field, Monsters with 7 fields or more of movement can do 2 fields. Monsters with 10 fields or more can do 3 fields (yes that one was extra for the goblins

)
3) If you have as weapon ranges both, Diagonal and Long/Extended (like, two heroquest fields), then you do "adjacent" and "diagonal" works in the same field; extended works in the neighbour field.
If you have only "adjacent" and "diagonal" as ranges, then "diagonal" can attack in the neighbour field and "adjacent" only your own field.
"ranged" / "Line of sight" is quite well defined in Zombicide. I would copy/paste the rule: Straight line of sights possible, but no diagonal line of sights. If the line is going through a door, you can "see" one field beyond the door and then full stop.
Conan Boards actually deliver a mechanism for this, and i would reuse it because there was a lot of thought put into: There are white dots in each field. If you can connect two dots, you have line of sight. If not, then not. Very simple.
Range "Same Room" (like Heroquest treasure/trap search) would work in line of sight (?)
"ranged magic" is indeed quite superfluous on those boards
"anywhere on the board" stays "anywhere on the board" with no change.
4) Traps are difficult. They cover one field in Heroquest, but in Zombicide / Conan fields that makes easily a 9 in 1 chance. If you put pit traps on a Zombicide or Conan board, you will find that easily there are fitting 8 or 9 traps in a field if the field is small like in Zombicide, and up to 22 if the field is big like in the worst examples in Conan.
Now.
4.1) Would we define that a trap is always placed by "the evils" in a way that it would work? Then one trap per field would be enough and it is auto-triggered if it is not disarmed.
4.2) Or would "the evils" always trap the entrance? Then the trap triggers only if you use THAT connection between two fields. (a trap would then actually be on a connection and not on a field)
4.3) Or would you roll a d6: If there is one trap, you get trapped on a 1. If there are 2 traps, you get speared on 1 or 2. If there are 4 traps, you fall down the hole on 1, 2, 3, 4.
4.4) Or would you use all the mechanics, as Quest designer choice?