The Chrony manual specified shooting about 4-6" above the unit at a distance far enough to avoid muzzle blast. The problem was the handgun blocked the view of the Chrony so it was hard to judge how high I was shooting above it. After an hour of shooting I was tired and put one through the Chrony.
Now, I tape a target to the back end of the Chrony with the bullseye about 6" above the box. This gives me a target to aim at, with a greater margin for error. So far, so good!
In sunny Arizona