ZDoom

When dealing with non-slopped 3D floors, you never have to worry much about where the model sector is. But when you slope it, you need to as the target takes on the plane at its own location. This makes moving either sector a pain, as you have to change the model sector's slope parameters to get the back the slope you had at the target. bv

What I suggest is allowing mappers to set that the target sector takes on the plane of the model as if its center and the model's are the same. In other words, if I angle the slope of the model's ceiling 45 degrees down to the north east, then its appearance at the target is the exact same.

This should be as simple as offsetting the x, y, in ax + by + cz + d = 0 to be at the center of the target sector ceiling/floor?

I'm not sure of the best way to present the option to mappers. Another flag in action 160, perhaps?

That's some really shitty way of doing it, actually. and will only cause problems with people not doing it right because they and the computer may be at odds where the center actually is!