Good point but even if that was the case he could have taken another 1/4 pill, a big glass of water and perform.
I know escorts who "evaluate the situation" after the meet the client, take the pill or not after. Chewing Viagra (instead of swallowing it) on an empty stomach as told by our resident Dr. @Unicorn is also a good way for it to make fast effect.
It takes 2 to tango and not all positions (legs up, sitting on it) are not possible with all body types of clients. Before PrEP I would always put the condom at the very last moment and after fingering with lub to get him ready. I always hated when guys would star searching for poppers right after I put on the condom and other diversions.