I did a sim with the CAA ops inspector on board and for thought I should only start the decent at the FAF. As in my IR rating test.
I got picked up for it as I ended up initially high as the FCOM said start down 0.3d before TOD.
IMHO this is not type specific. As you said: an IR item. That is not type specific. Most airlines I flew for, using V/S, started down at -0.3nm. I then 'graduated' to a VNAV/LNAV airline. Guess what, the a/c starts to reduce thrust and gently nose over just before the FAF. Perfect. Guess what: the same XAA said that on a V/S approach you could NOT select the descent before the FAF. Consequent is you have to select a higher than normal ROD and then assess when you are on the path to reduce ROD to maintain the path. Talk about making a difficult job even more so. It increases the workload of both PF & PM close to the runway. WHY?
In this case it is not type specific it is XAA specific. Why should you operate the a/c in a different way manually than when the automatics control it? Simple!