I see your point with the snowball effect, trouble is a static value against a potentially decreasing variable value give problems. It may become wholly possible for 2 units to damage each other so much that neither unit would be able to hurt the other without unusually high rolls. If I may hazard a thought here...are you planning on giving defence bonuses for terrain, cover, etc? If so, the static vs variable dynamic could be levelled nicely with the application of strategy. Dunno enough about the system to comment though!