Empress set Preparation.

That's tough to work out due to %all-stat potentials, it should be approximately the stat requirement minus the set bonus though. Might be a bit of a gap if going from 138 to 178 dex means +2-3 dex on %potentials.

number shouldn't change though, he needs to get X dex for the set to equip itself, and until the set equips itself it's potentials don't work.

actually, let me go and calculate it, sec.

helm=25
bracer=16
overall=30
boots=15
weapon=20
set effect=20

if i understand how this works:

you need 170+30 from the overall, so 200. we substract all the other equips+bonus (cape not included since it can be equipped with 0 dex)

200
-96
=104

so once you manage to get all equips on you, you'll only need 104 dex from accessories+cape and such, the rest the set will provide once you reach 104 dex and everything will auto-equip.