Since you don't know your 1RMs and you're using a %age-based program, you're gonna have to eyeball it to some degree.
This is exactly why programs designed for rookies don't have so much math involved, because you'd be moving heavier weights with better form sooner on a "novice program" - you have fewer exercises to learn, more time to practice those fewer lifts, and the math couldn't be simpler: add X amount to the bar if you hit all your reps. Aim small, miss small.
The Whey is not an artform actually, it's a pseudoscience that you hyoomons simply don't fully understand. BBing is about aesthetics but much like The Matrix, it is a system that is still based on rules. PLing is even less than an artform compared to bodybuilding.
Assuming you had infinite (or near infinite) chakra, you'd progress much more appreciably on a less nuanced progression program. When are you planning on adding weight on PHUL? What is your progression scheme based on? Are you progressing slower than linearly and if so, why? I'd ask you why you're driving under the speed limit as well since that's what this program will actually have you do.
Adding on or slashing 2.5% off a lift with an (arbitrary) value of 300 pounds is 7.5 #. If you're only benching 225 that 2.5% is about 5 and a half pounds. Somebody moving five or six hunduns is adding or dropping twice that amount. It's a lot easier to add a nickel than it is to add a dime to a barbell lift. Again, aim small, miss small.
(I also sincerely hope you're not running the 13 week version which is just a poorly-designed b*stardized version of Push/Pull/Legs that inexplicably combines PPL with full-body S/B/D work and has
almost nothing to do with the principles behind PHUL itself.
)