In my early days, I looked hard for a formula for lip length and width, it was the engineer in me. But alas, I failed.
A sharp edge on the front face gives a stronger action, not so sure it is enough for you to notice.
The thing is that every feature affects lip length; length and width of back, position and angle of lip, position of COG, and any other feature that I fail to mention.
I make the lip a tad too big and trim it back until I get what I am looking for.
Dave