I make the lower outside corners or sometimes the outside edges of the rounded lip slightly wider than the body of the bait. Probably 10 to 25% wider. I originally modeled it similar to the 3:16 Wake Jr. bait and also the AC Plug Minnow.
It wakes well with a nice "V" wake in the water and makes a nice wood knock as it does so. My lips are made from lexan by hand. Sometimes with too much hard walk the bait is too clunky or mechanical. It seems best if you can reduce it and make it wake more fluidly if that makes any sense. If you get your bait all sealed up including the lip slot, you can test several different lips by taping the portion of the bill so there is a snug fit in the lip slot for testing.
Barry