Piratepete,
Did the OP mention MEDIUM braking action?
No,he just mentioned WET.
So,again.....a WET runway is a runway which appears reflecting with no standing water,3 mm or less of water.BRAKING ACTION GOOD 0.4 or more.
Now, a SLIPPERY runway is one on which,braking performance is less than on a WET one and Braking action is reported as less than GOOD..(below 0.4).
You are saying that a WET runway is equivalent to a slippery runway when the braking action is MEDIUM...
You can not define a runway of braking action Medium as WET.
If the braking action is reported as MEDIUM then the runway is SLIPPERY and not WET.
SLIPPERY data then must be used,
So for the OP,a WET runway needs no weight adjustment if perf is calculated via the FCOM(PI).