So you can set the attack range of a melee to 120 if it's at 100. But it will not really matter...
But you can set a melee unit to range by adding range and adding missile and changing attack type.
I made combat acquisition range to 5. Can it be responsible to cause this any problem?
5 range is very short. You can toggle a grid in the editor by pressing G, the smallest squares are 32x32, medium are 128x128, large ones are 512x512.
I didn't want the units to get into combat automatically so put it less
acquisition range must never be less than attack range even for ranged heroes set both of them 200 and it will work
acquisition range is like a max range. If you have 200 acquisition range and 500 attack range that unit can only attack things within the 200 range. It will not have 500 range for attacks.