I found that, but the original indicates slight ramping covering 4 squares so that doesn't fit too well either. Adding the ramp symbol to all 4 squares sort of makes it look very steep.
The text for room 12 description combined with the isometric maps should illustrate this well enough.
BTW, I assume you have generally avoided adding "muliti square" symbols as much as possible in MapMatic since you could quickly end up with huge number of symbol variants.
