Mark is your post 7% measurement directly after the prewash or after the 2 hour settle?
I don't get what you're asking mate.
Perhaps I'm misunderstanding your process?
Do you?
1 - add prewash water
2 - mix prewash water
3 - turn off pump
4 - settle and remove glycerol
5 - stand for two hours
6 - remove any extra settled glycerol
7 - start first wash
In which case if you sample the soap PPM after step 4 and 6 there might be a difference
Or do you leave the settling glycerol in for the whole two hours, then take a sample?
I hope you see what I mean!