Note that Back Course ILS is a lot more sensitive than a front course. Worth defining a Final Approach Fix then RW MAP or THOLD coordinate in the FMS and flying LNAV, whilst using the raw display as a reference for the procedure.
Every BC ILS I have witnessed as PNF in the sim, flown using the heading bug, results in the PF blowing through 1 dot during the latter stages of the approach.
Suggest you have a go on your next Sim training or request if your training program would allow for it.