Scenarios deploying units underwater.

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I have recently been working with making my own scenarios and the one I am currently working on requires one side start with several mechs underwater. If i use the coordinates to have a given unit start in that hex it seems to begin the game 'walking on water' rather than submerged and unable to move in any other mode but Jumping. Is there a way to have it recognize that it should be placed in the terrain rather than over it as it does when you select a water hex during deployment?

Apologies if this is something simple or discussed elsewhere but I haven't been able to find anything on it. Thanks in advance.