I would have guessed the same as others that it was interactions between the nozzle and the bed or some texture on the bed. Especially since we don’t see any normal extrusion lines which are normal on the first layer.
Since you’re confident it’s not, are there artifacts elsewhere on your prints that might be a clue? Is there anything going on with your nozzle? Maybe some wear, chips,or inconsistent flow? If you print just the first layer what does it look like from the top? Does it help describe what we’re seeing?
I’m confused. Did I miss understand your wording?
100 - 77 = 23; 23% < 33%
77 - 10 = 67 point lead
Admittedly the way we talk about a “point lead” is confusing and it’s always useful to look at what the real numbers are and what they actually mean.