In the interest of making things interesting, let me propose that people are free to adjust the height of the entrances in the reverse levels, within reason of course.
I'm going to try to define "within reason" more rigorously below:
- you cannot move it so much that the lemmings start out totally in a different area from where the original exit was situated (eg. below the terrain the exit sits on so that the lemmings land on someplace else altogether, or above some higher overhead terrain)
- if the exit trigger was fully buried in terrain (ie. requires terrain removal to expose the trigger for use), then the corresponding entrance must be placed such that lemmings come out stuck inside the terrain. I would actually go as far as to say that the lemmings should come out at a vertical position ("position" as defined by Simon's definition of "effective coordinate" in
this post) that's within the y range of the exit trigger, or lower if necessary for them to start stuck.
- conversely, if the exit trigger was not fully buried, then the corresponding entrance must be high enough that the lemmings come out at or above ground level. Even slightly lowering the start position into the ground (without causing the lemmings to start off stuck) should be prohibited. In PC Lemmmings, the lemming's starting y-position is the y coordinate of the entrance object, plus 14 (larger y means lower on the screen).
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Basically, the idea I want to capture is that the lemmings should end up landing on a location as close to the original exit's trigger area as possible, but give some freedom on the actual fall height, as that doesn't obviously map to any attributes of the original exit object, and therefore might as well be made a part of your strategy to pick a fall height that works best for your solution.