chasing some advise/ insight into the fitment of the quaife qdh12b front diff to suit the 8mr

I currently have my car in a shop getting mine fitted, they have advised me that the right hand side shaft that goes into it doesn't go in correctly as it would with the stock diff, they are saying that inside the diff there is an 20mm difference in depth for the shaft to go into, so the circlip on the end isn't locking it in.

have anyone experienced this before? do I need a different shaft?

thank you for any assistance you can give