Great to hear you're still at it. As I tried to convey above, it's a great product, these are just the two areas where it could gain some. I am aware that the cloud shadows are tricky to inject... having a smaller radius could be a short term solution.
Funny thing is, my test flight for SkyMaxx is an afternoon flight from KATL to KMCO. You have certainly nailed these low but big, puffy cumulus that are scattared in central FL. The problem with the cumolonimbus is that they're so seperated. I'd expect larger, darker areas of heavier clouds to surround them, Right now flying in FL's current weather (in X-Plane with SMP & RWC), you have rather standard cumulus, and then these killer clouds here and there. In these situations, I would expect a larger thunderstorm area.