I FOUND IT! 3420 is the Perception you want for your MIN/BTN retainers!

[Caimie_Tsukino]

Data on Fisher Retainers:

2320 perception:
15 lvl 83 Spiny King Crab
12 lvl 84 Dream Pickle
7 lvl 86 Protomyke #987
12 lvl 87 Grey Mullet
9 lvl 88 Shallows Cod
9 lvl 88 Rummy-nosed Tetra

2342 perception:
15 lvl 83 Spiny King Crab
15 lvl 84 Dream Pickle
7 lvl 86 Protomyke #987
12 lvl 87 Grey Mullet
9 lvl 88 Shallows Cod
9 lvl 88 Rummy-nosed Tetra

2362 perception:
15 lvl 83 Spiny King Crab
15 lvl 84 Dream Pickle
7 lvl 86 Protomyke #987
12 lvl 87 Grey Mullet
12 lvl 88 Shallows Cod
12 lvl 88 Rummy-nosed Tetra

... So the optimal perception appears to be somewhere between 2343 and 2362. Once again, just need Grade 8 or lower materia. No Grade 9 / 10 materia needed.