I avoid the straight down shots.
No chance to hit both lungs, and with an arrow that should be the goal.
If you spine him, a second shot will be easy, but hitting just one lung can make for a LONG day, and the heart is pretty well protected from directly above.

To avoid straight down shots, I try to set up at least 10 yards to the side of a trail, and not too far up in the air so that the angle won't be so steep. A shootermight also wait until the deer moves a bit further away, and then make a noise to get the deer to turn before shooting.

There are far worse shots to be taken with a bow than the one we are discussing. At least you can hit vitals shooting straight down, but I still avoid them.