Post fracture can be a very slow rehab. If your worried about the bone chip moving around then you should visit your GP to get it re XRay'd to see wether it is healed now. I would have thought you would have had this already when you came out of immobilisation?
Post immobilisation regaining ROM is painful and you can expect some slight swelling as I think you've been out of the boot now for 1 month?
If you are unhappy with your current progress then when speaking to your physio and request a 2nd opinion within the physio clinic. Generally if the physio is a good one they will understand and be happy to obligue.
My thoughts is that the damage sounds extensive enough and if you were immobilised for 4 months then your current progress could be considered normal.

Good luck.