Just took a look at the description of minime: "In version 1.1.0, the character scaler part of the mod has been improved: Values from the attack parameters of personal weapons are scaled as well, so the muzzle flare won't be ridiculously off the gun." I think this is probably the problem
Hi, I'm the author of minime and found this thread by mere chance. It doesn't seem reasonable that bullets should miss a target just because they're flying too high. Remember, this is Factorio where you have no Z-axis! Height shouldn't matter at all, as long as there are biters in the direction where you shoot and they are within your weapon's range, you'll hit them. The scaling is just a visual thing, it shouldn't affect anything besides the character's appearance.
Also, I've just tried to go hunting biters. One time, I scaled the character up to 200%, after that I scaled it down to 30%. I could kill all biters I shot at, the scale factor made no difference at all.
@AlexiaNoir: Could you provide a saved game, perhaps? This way, we could sync our mods against your saved game and try to figure out what really causes your problem.