When you give the coordinates for positionCell, does the Z height value refer to the center of the object (in this case, the player), the lowest point of the object, or the highest point of the object? I'm getting some unpredictable results when placing the player on a ramp in front of the main door of Tel Uvirith: sometimes the player falls through the ramp down to the dirt level below.

I wonder if the race height multiplier of the player character is a factor here?

I could inch up the z-height of the coordinates, but at some point, it's going to start to look strange when the player falls from a few feet up.

In the case of the player it is the feet. In the case of objects it is the centre as defined in the modelling program.

I spot-checked some vanilla NPC placements, and they're mostly a foot or so in the air above the floor. Anyway, I nudged the z height up a bit in my case, and it seems to help. There's a slightly noticeable drop, but I can rationalize that from a roleplaying standpoint as simple teleport disorientation.