When I suggested looking at successful commercial lures, it was not only to see what angle the lip sits at, it was also to do a float test to see how to ballast them. Seeing how a lure sits in the water says a lot about how it's weighted, and what angle of attack it needs initially to perform.
All deep diving floaters sit nose down at rest. Aside from esthetics, having the flat, 0 degree lip already pointed down lets the lure begin to dive immediately, and allows the 0 degree lip angle to work.
Shallow lures typically float horizontal, since their lips are at 45+- degrees, and dig into the water without any help from the atitude of the lure. A lure with a 0 degree lip angle that sits horizontal (level) would struggle to dive, because the lip isn't catching enough water to initiate the dive.
In lures with movable ballast, to aid in casting, the diving lures have a system that's oriented from low in the belly to high in the tail, so the ballast moves to the tail on the cast, and then drops back down to the belly, lowering the nose and lip, once it lands.