Well, many studies have proven that the corners of any
screen are the easiest places to mouse to. But I don't understand why you are accidentally hitting that corner of, apparently, lots of
windows.
There's just nothing up there other than those arrows which I never use, intentionally, either. I don't understand why you're anywhere near that spot so much.
MaxMeuns is a very old System Pref that allows just about anything you want to appear at any or all the four screen corners; with or without modifier keys. It's been around almost from the beginning of OS X and I don't think it has been supported in many years. But it still works perfectly in every version of the OS I've ever had.
I have the System Prefs set to the upper, right-hand corner.
This allows me to select the Pref I want before even opening the System Prefs window.
The lower, right-hand corner has a few apps I tend to open often but not constantly leave open.
Since the 'buttons' are in the corners, it's extremely easy to get there, even with a touchpad. Once you hit any side, the only movement left is along that side till you hit the corner. Once there, you have to change at least one of the directions you were moving (Up/Down or Left/Right). Again, there just aren't ever any windows covering the Menu Bar (top of screen) and only extremely rarely the bottom, right-hand corner. I do get frustrated with the Dock opening when I mouse down there, however. Fortunately, it doesn't extend all the way to the corner so I don't actually hit anything on it.
My second suggestion, since you seem unwilling to just do things like I do, is to tilt your monitor at least 30° to the left. I think that will make most of your diagonal moves more horizontal on the monitor, at least...