I would mod the accuracy (for all relevant units), as range and damage shouldn't be what at end should differ signficantly (if the weapons are compairable), but instead the ability to actually intentionally hit a target even if at maximum efficient range while mortal shouldn't.
See here under the "For modders"-box
http://www.twcenter.net/forums/showt...)-with-Trailer
EDIT: Do you btw know what the range in the game is counted in? Is 300 the same as [ca] 300 years or meter?