I did a dmg/hit ratio simulator. 1000 is definately not enough, i´m running at like 100k for each distance and even there are differences.

the area calculation would be the right way if you want a proper percentage. but its really hard to do.

I meant per situation. Targets have different profile in the game (sectoids are short, soldiers are tall, etc.). At the same distance, the same shooter with the same gun will get different percentages depending on the target, your elevation and any partial cover that obscures the target.

If there is some button in game that allows you to run a 1000 dummy aimed shots, the result should accurate within 1-2 percent of the actual hit percentage. It would be even better, if, instead of using the RNG, you could just test for all possible RNG values in the formula. Of course I didn't actually test it so you are probably right.

Calculating the area would be easy if you consider only ball shapes, but pretty hard if you want to calculate it for any shape.