This is the upper end of tip range, or even wishful thinking. I have been asked for such amounts (and more), but generally get boys for 20 USD (i.e. I never agreed on more than 20 USD in Cambodia, but tipped some exceptional ones more).
Recent (two days ago) data point to support my numbers is Chanak Spa, 1 hour massage 10 USD and expected tip for happy ending 20 USD (I asked manager before massage, and anyway 20 is my experience of several years, and the masseur said "thank you so much"). General recommendation for Chanak Spa, I was happy with how they run their business (available boys are presented in person behind a glass wall and curtain - shirtless would be nice, but even fully dressed a big step up from choosing from pictures), the massage and the happy ending. Location on google maps is slightly wrong, it's close to the center of street 470 and not at the end, I submitted correction.