Offseason Training Results

Does anyone know if there is any logic to the offseason training results? I've had underclassmen play 85-95% of the snaps and put up good stats but have minimal 1-3 OVR improvement while other underclassmen who have played minimal amount or not at all that have had a significant boost to their Overall. I had an FS that played 0 snaps and wasnt redshirted go from low 70s to 84 OVR and he has a normal dev trait.

I guess Im just confused if its all just a crapshoot or if there is anything I should do differently? If I have certain players I want to play with and improve but end up with minimal progress while random benchwarmers take a giant leap then I dont really see the point