Under UPC the laundry standpipe p-trap must be: 6" <= floor <= 18"
Q1: where is the measurement taken from w/ regard to the p-trap? In Peter Hemp's book it shows it as the connection point between the standpipe (above) and the p-trap (as opposed to the weir or dead bottom of the p-trap, to name to other obvious points of reference). Is Hemp's drawing correct?

Under UPC the laundry standpipe top must be: 18" <= p-trap <= 30"
Q2: is the aim of these two restrictions to end up with the standpipe at 36"? One interpretation would be that if the p-trap is 6" from floor, standpipe should be 30" from p-trap, and if p-trap is 18" from floor standpipe should be 18" from p-trap... this is NOT what the code says, but is that what it means to say?

OR to put it another way...
Q3+: what is the recommended height above the floor for the top of the standpipe? Should it be above the flood level of the washer (as I've seen mentioned in one resource)? Can it be "hidden" behind the machine (for aesthetics) or does it need/want to be above the machine?

Thanks.