BTW, I must insist that your waiting time (approx. 3h) is too much for double coating. Just do it as I described; you'll gain a lot of time + the second coating will go very smoothly thanks to the paper's very relaxed fibers. (OTOH, be gentle: the surface is much more delicate when moist/wet!)
A last note: As a rule of thumb start with using 0.2ml sensitizer per 10 sq in. Work out the correct amnt. of sensitizer for your coating method/style/speed ect. from there. You need a sensitizer amnt. that is plenty enough to coat the given area (without hurry!), but also not too much to cause pooling and force you to overbrush...