Real Vs Bayern

[one]

I'm also really not sure where they have drawn the defensive line there, it almost seems to be at the defender's wrist and is well beyond the armpit level.

It's not a thick line. It's a thin vertical plane. It's just a really badly drawn low budget graphics. Everything to the right of it is meant to be visible and everything to the left hidden. The bit that overlaps the wrist is actually the bit of the plane on the ground aligning to the defender's back of the foot.

The line has been drawn in the right place - it's the top of #22's arm. My issue is that in the photo Mazraoui's right knee looks to be level with de Ligt's, but isn't showing when the white plane appears.

It's actually there if you look close enough. If the white plane is drawn accurately this should have been onside. There is more of the defender's foot to the right of the plane than the attacker's knee. Or worse case scenario, it's level.