Shielding Success Rates Mystery

Standing still works because the enemy gun rotation happens after the bullet is fired, so they shoot from a position of 1 tick ago but use their aim from 2 ticks ago. So if they are moving their angle to you changes and they don't quite shoot at your centre, meaning that you can get your bullet line to intersect with theirs because your bullet comes from your centre (which they aren't aiming for). This is also why it stops working when they stand still, because their last position relative to you lines up with their current position relative to you so you end up shooting parallel.

I'm trying to figure out why my super-advanced precise circle-line intersection methods are failing so horribly at getting shield hits. I get one every now and again, but nothing like what I should be based on the maths and shield size I'm calculating, and nothing like the 3/4 of bullets that a simple linear projection + bullet power adaptation was getting.