A Mek's elevation is measured from the hex's level, so one wading in water stands at minus the depth. Placing it at zero left it at an elevation `isElevationValid` refuses, and `isMoveLegal` then rejected every step out of the hex - a turn included - so the unit read as unable to move at all. `Entity.fixElevation` is MegaMek's own repair for this. With it the corpus takes a third board, `Map Set 2/16x17 Lake Area`, whose water at depths one to three and level 4 spur put the two cost model arms the first two boards could not reach under the comparison.