From there on climbing ranks didn't become harder anymore.²

see Levels of Monks for details

Readjusting those deltas to constant grow would give you your extra levels in a natural way, without needing to invent new ranks.°

This would actually mean a demotion, now for real.³

But I wouldn't care.

Tho I think the monastery has more urgent problems...

°) Here a rough sketch. The deltas would of course need to be properly rounded to steps modulo 1000

  DB<4> say join ':', $_,$d*=1.25,$xp+=$d for 23..28
23:12500:52500
24:15625:68125
25:19531.25:87656.25
26:24414.0625:112070.3125
27:30517.578125:142587.890625
28:38146.97265625:180734.86328125
[download]

as you can see, even BUK would need to reincarnate to reach (28) patriarch again ;-)

²) well it was far easier in the old times to gather XP, but that's not the point here

³) loss of rank would only happen to less than 20 monks actually