Thank you for your help.
But, unfortunately, now I am even more baffled with the game. Don't get me wrong. I think this game has several great features, but combat system ... I don't know. I was actually hoping you guys would say that the entire skill has to land on the required side to hit. That would mean I have a L2P issue.
After I got home yesterday, I deliberately played only for test purposes, and especially Lancer combat is where I felt completely out of touch with what was happening on the screen. Like Estellios said: "you may actually be hitting the wrong side when you think you are hitting the rear or flank". How is that possible?
Besides that constant delay that they implemented into almost everything, combat system looks to be working by the principle "you just press your buttons and something will happen. Just maybe not the exact thing you thought you've done".
Surprising, really.