Is there a way to mod troops to be, say, 30 ft tall, or anything else? This would prevent situations like the below screenshot where players put a bunch of lines behind each other and all of them get to shoot.

OK, so it can't be modded right now. We hope sometime it will be.The difference in elevation needed to allow shoot-over is hard coded. However, you have to remember that the sprites scale to about 12 ft tall, to looks are deceiving.
-Jim
I agree that, if adjusting firing over is not possible, disallowing all firing over would be preferable. IF:There are more reasons than just trigonometry that lines shouldn't be able to fire over each other. It would be better if they could *never* fire over each other, than what we have now.