i don't know of anyways to account for extra range.
what MIGHT work is if you were to place your armies like normal with 3 ranges and see what you kill in the first round, if all your range that's going to be attacking is 4 range then you can simply ignore the deaths on your side and say that's how many i will kill on the first round and from then subtract the units dead from the other side and do the sim again this time all your ranges will be 3 ranges on both sides, and then you can see how many you will kill in general. let me give you a scenario, if this method actually works, i never tried it
say you have 400 range and 300 armor(all your range have 4 range----your armor has standard stats)
the other side has 500 range and 200 armor
first enter this like you would normally enter it.
so when you do the sim you find out you kill 200 armor and 100 range of his. an he kill all 300 armor of yours. (made it up)
so at this point you know you have 4 ranges and your opponent doesn't so you ignore your deaths and next time you do a sim it will be like this:
you have 400 range with 300 armor still because the other range has not had a chance to fire
and on the opponent side will have 300 range and no armor, and then you see what you get.
if you have range 5 units you can go one more round on the sim and ignore your deaths. like i did above.
Note: this only takes into account the range not the extra damage and health your units will have by the time your units have reached range 4 or 5. so you can consider this as minimal kills.
Hope this helps.