Fun fact - in unmodded XCOM (well, XCOM 2 at least, not sure which one you're talking about here), enemies have - unlike your troops - absolutely *no* range penalties whatsoever. That lowly advent trooper you ignored will have exactly the same to hit% regardless of whether he's sitting on the other side of your trooper's cover, or sniping them from the edge of their line of sight.
That being said 85% is not 100%, and in fact it's a 3 in 20 chance of missing. Anyone who played D&D will tell you that happens more often than you'd like

It does work both ways though, even if it might not seem so. Just yesterday I had a smoke-covered grenadier face a quarted of pissed archons. Didn't look good, all four went for melee, 64% chance... three misses in a row, fourth one did hit but that she could manage
All in all I'm squarely in "love XCOM 2 to pieces" camp, but @
sgt_pinback is somwheat right, in the sense that XCOM 2 line of sight is messed up sometimes. I'm going to challenge the "never ran well" a bit - the PC version of WotC is a major preformance improvement.