I wouldn't shoot under 90 either.
With Vetsulin, I wouldn't shoot under 150. Probably not under 200, until I had a lot more test data and knew what my cat would respond for the cycle.
Is Felix being fed at least 20-30 minutes before the insulin shot? That is important to do with Vetsulin (aka Caninsulin) because it onsets faster and harder than some other insulins.