This mainly becomes an issue on alien ships. When I have a soldier on higher ground, if I want to move to the edge of the higher ground it moves the box to the lower floor. It’s very difficult and sometimes impossible to get to certain tiles because it drops down to the next level.
Is there a way to force the movement target to stay on the current plane?
You can control which floor you’re going to using the mouse wheel.
Alien ships, however, do have the annoying tendency to have strange architecture which confuses the floor-selection mechanism. My work-around is to play with both the mouse-wheel to control the floor and q and e to control the angle, until I get my cursor in a location where there’s nothing behind it, so it has to choose the upper floor.
The same can be done with the dpad on consoles or on a gamepad for windows.