How long ago was it installed?
You could look into a MFGC or RSP, which could help
If it helps, you can add a delay to your PM3 commands to give you some time to position the PM3 before it tries to read: How to add a delay to Proxmark3 commands for implantees
But for the most part it comes down to just learning the placement and experimentation. Playing with the xFD’s that came with your implant, as well as the hf tune and lf tune commands on your PM3 can help you find that sweet spot