Realistic accuracy without brutal AI?

[Delian]

100%+ accuracy in mods like XCF sometimes affects damage so it's crucial to keep.

It does not. Accuracy formula and damage formula of a weapon are independent of each other. You must've misunderstood something.

Technically, OXC has a hidden RNG built into firing trajectory generator, which is why it's possible to miss 100% accuracy shots. You could say that all shots are already 95% chance-to-hit shots. That's why there was nothing wrong with a 95% cap, assuming Realistic Accuracy bypasses the original trajectory RNG.

[jnarical]

One of the selling points of this feature is "if you can see it you can shoot it"

Done. Will be added in next release.
Also, changed wording for RA options, to make them shorter / clearer.

[Stormtrooper]

OMG yes I'm so happy thank you so much you're awesome this feature is awesome everything is awesome.

[jnarical]

Horizontal vs vertical spread - another suggestion of mine is to have the latter lowered compared to the former

Done, now fire cone is elliptical, I added to horizontal spread a little (x1.2) and reduced vertical (x0.65)
I'll do my best to test it better tomorrow. Next release should be in a couple of days, and if I won't be too lazy and slow - I'll expose all RA-related variables to yaml file, so modders could edit them. And tuning them will be up to you 

100%+ shots...  but 95% cap is something I guess

Done. I moved RA config to ruleset, you can either edit it directly (openxcom/standart/xcom1/realisticAccuracy.rul) or create small mod.

Upd:
Revamped spread calculation, made the whole set of parameters and algorithm itself much more clear for understanding and editing. Now testing it.