So you mean if a monster is on floor z:3 he can attack you if u are at floor z:5?
I think he means for example, that if you are on a bridge and one floor below you is a minotaur archer, the minotaur archer is able to shoot you from distance.
thats pretty hard to make...imo just skip this idea. Even if you gonna modify functions like canDoCombat, canSee~, isSightClear~ to allow multifloor hits, its really hard to realize when monsters are able to hit and when they are not. Basic thoughts are about:
-if floor > 7 - false;
-if attack is melee - false;
-if got a tile above creature - false;
erm, just skip this, thats pretty hard to make it bug free imo...
a, nvm. Not possible with your skills, as this is not 'some source editing'.