@Scrugy51 Couldn't really explain, tbh.
If I have the time and remember, perhaps I could make an example?
It could be a few weeks, though, especially since I'm going on a ~week long vacation soon, and I won't be able to play at all, will to do so or not.

@Graingy uhm..
I kinda understand but how do I fix the gap on this certain build?

@Scrugy51 Hmm.
Okay, so...
How do I put this...
Okay, so you have your section that you want to have hold a canopy.
It's inset.
The issue is that it's at an angle.
You want to find the fill % that reaches and "seals" just with the canopy.
To have it flat, you'll need another fuselage to be the "slant".
The issue is that in yours, the fuselage of the cockpit is the same as the fuselage that cuts down.
Am I making sense?
Not to myself, I'm not.

@Graingy how do you fix the gap between the canopy and fuselage

okey so I took a look and now it's time for some unsolicited critique(TM):
First off, about how the plane performs: Perhaps you noticed, but for a reason I cannot tell, the lift and mass are off-center. More looking would probably reveal the cause, but I am lazy. Otherwise, seems to fly fine.
Second off, I could have sworn I mentioned this but I apparently hadn't: fuselage fill slopes. While not bad, per se, in my opinion it looks a bit rough around the edges (literally. It got edges). I haven't paid that close attention to what builders more skilled than myself do, but personally I tend to use the method of making the back (or front, if your using the method to make a fancier nose) end of the fuselage smaller, and then using the rise feature to make it bend the way you want. I believe it's around 0.5 different in width for every 0.25 in run, if you want the top/bottom to be flat.
As for the cockpit, another hollow fuselage in the middle should sort it out well, making it more flat and without the gap.
Also, the landing gear clipping into the cockpit leg room is a bit... jarring. Gives a good sense of scale, though :)
Moving into more nit-picky territory:
The twin miniguns do come off as a bit unrealistic. Rotary guns irl tend to have large ammunition drums, and while that of course isn't a problem in SP, having one connected to an unused space (i.e. a fuselage component that doesn't contain any gear or other things) instead of sitting on its own does make it a lot more believable, since it's easier to imagine it actually existed instead of having magic ammunition reserves.
But this plane isn't that bad of an offender, so I suppose it's okay.
That was all that comes to mind at the moment. Sorry if this comes off as rude, I really do just want to help you along (and I don't know how to not be patronizing, evidently...)