What is the hit chance when your Fighter is attacking from behind?
60%+ but I still miss most of the time. I'm not trying to be rude but can you trying to please understand what I'm complaining about here? The game's numbers are worthless. Even with an 85% chance I still missed, reloaded, missed again, reloaded and missed a third time. If that was an isolated occurrence it would be bad luck. It is not an isolated occurrence. That is the crux of the complaint. It needs balancing better.
I understand what you're complaining about, right from your original post. Those things you described; many of us have experienced them to some degree. But whether you think we truly understand you or not is irrelevant, since your own enjoyment of the combat is what truly matters at the end of the day, isn't it?
A Larian employee will probably look at your post and file it away for future reference, and any change that comes from it won't happen for the next few months at least.
This is why most of our replies focus on how to get you to play better, since Larian isn't going to change the combat any time soon.
On that note, getting only 60% chance to hit even while attacking from behind is really low. There's something else going on. If you wish to fix this, you might want to take a screen shot and post it here so we can have a look at it.