Quoted from yaksplat:The lower corners are the vulnerable spot. You don't want water to wick up the cut in the tyvek onto the bare wood sill.
This times 100. I just finished helping a friend replace some windows that were installed less than 10 years ago and they were under overhangs and fairly protected. Building was wrapped, but they did a shitty job of sealing the window corners and not only ruined the windows, but we also had to replace some framing as well. What should have been a couple day job, turned into almost 2 weeks and a lot more money.