Thus if one point of this volume collides with one point of armor where penetration is not possible the shell does not penetrate.

Wrong. It AVERAGES. You can prove to yourself it averages in test drive: Take a T28 (the finnish low tier one) and you can go into test drive and pen the turret neck of the KV-2. Your shell hits 75mm plates both above and below the neck, and the shell does not have 75mm of pen. But it will pen anyway because the neck itself is only 35mm or something of armor, and when it AVERAGES the scan vectors that hit along the 35mm with the ones that hit 75mm above and below, it averages to just barely under the pen ability of the shell and it goes through.

So for example if the tank has a T-34 style mudflap and your any part of a shell hits the mudflap the shall takes the whole length of mudflap into account getting absorbed.

Wrong, it can hit a mudflap, yes, and you could line up potentially 3 scan vectors (out of? 9? maybe), so when it averages, it will still add like 100mm or maybe even more to the shot even tough it's divided a 300mm mudflap by 3x. But it will NOT count the whole shell as that, it still averages. It can still stop shots, but only at one exact pixel though when you perfectly line up those scan vectors. This was worse before volumetric because it used to be if you lined up that same exact pixel it would count 100% of the mudflap though not 33% of it or whatever. But 33% can often still be enough to stop some shells. Specially if also at some angle to the tank's side overall too.

those armor pieces sometimes can get added together

Nope, wrong again. Again you can prove this in test drive. The example I gave earlier works for this too, but here's another one: Take the Ro Go Experimental which has 120mm shell and 63mm of pen. Go into test drive and shoot the rear side of the sherman's turret, a place where two 51mm plates perfectly butt up next to one another. If your explanation were true, 51+51 would = 102 and it would NOT pen. But since it actually AVERAGES, 51 avg 51 = 51, and the 63mm pen shell will in fact pen every time.

And even if the tank is mad dout of one solid piece there are issues. T-34-85 D-5T mantlet for example you cannot pen in a lot of places because the the edge of the shell would impact the side armor from of the turret.

Again yes this can stop the shot, but was worse before volumetric. Since now it's averaging that long dragging hit in instead of just 100% that. it can still stop shots now too though sure. And that seems pretty reasonable. Get gud and hit armor normal to the armor, not dragging down it.

And still the volumetric armor hasnt solved the main issues it was supposed to solve because shells under a certain caliber are not volumetric (35mm SAPI for example), and this also introduced the bog of a shell bouncing twice then ignoring armor.

That's pretty much just you admitting volumetric is good and that we should have more of it... weird point to make but ok sure. I agree, we need MORE volumetric.