Are you searching for brighter or darker tone?
The big thing I have been following is internal capacitance of pickups, higher capacitance yields darker "muddy" tones and higher capacitance comes from more perfectly laying down the wire layers. The more scatter or the looser the coil the lower the capacitance and brighter the output. As a player I can always turn up the tone knob to get darker, but there is no bright knob. Maybe that helps some.
The other avenue, since you are testing bobbin shapes, is packaging the P90 in a standard humbucker cavity, many many players have humbuckers and miss out on the charms of a P90. Lately I have been thinking the guitar world gave up a lot of good tones in the trade-off with humbuckers.
Recently I repaired a Magnum branded late 70s/early 80s LP guitar (store brand ghost built by Ibanez Japan, bent plywood 'carve top' with two solid wood layers behind it). It needed a fret level and complete deep setup. I had bought it some time ago and a guy recently was searching for one like it to regain his youth with his first guitar. The one I had was the deluxe version with a little different headstock logo treatment but the same color and otherwise identical to what he started on.
It had the common P90 type of design packaged to look like covered humbuckers. After setup and pickup balancing the guitar sounded exactly like my dual P90 PRS SE guitar that I went back to back with on the same amp same settings and ... pretty amazing, really. Made me want to keep the thing.
When I sold the guitar to the guy and told him how it was hard to part with due to the tone, we laughed about how the guitar must have sounded terrible as a kid with a kid's amp. He plugged it in back home on his grown-up amp and texted me how great the guitar sounded and played.
So, I'd suggest trying to shoot for the humbucker package size so more folks can try out the P90-type of tones.