A very nice read, thank you.
I note the original TP was 2mm but you removed 'the plug' to reveal the 4mm. Then the high power issues set in.
I wonder: could you not have tinkered with the TP to get what you wanted ... maybe trying 3mm or 2.5mm etc? I am sure there must be a good reason ....
Interestingly my daughter has a 52 at about 11.5 and it is really quite pleasant. I do not know the TP size but can say that we have never changed it.
Maybe way off topic but I had a 'Chuntsman' ... Chinese version of the Huntsman Mk2 ... that had consistency and low output issues. The TP was quite small (sorry can't remember now, maybe 2.6mm?) so I experimented with ports of different diameter ... they were simple delrin, drop in units easily made on the mini lathe. I seem to recall that 3.5mm went hot and I settled eventually on maybe 3mm for a nice consistent 11ftlb.
Cheers, Phil