In my opinion, you cannot get too close to birds, unless you have no cover.

In your situation, you really have to bite your lip and wait to call until the bird hits the ground. If you hadn't called, that gobbler might have flown down right into your killing zone, just as a matter of normal routine.

More times than not, a gobbler can see the nearby roosted hens. Hence, when you call to him in the tree, at that close range, they oftentimes get spooked especially if they have been hunted hard (as this one probably has been).

Next time, try not calling till he's on the ground, and hopefully you'll be carrying him out over the shoulder...good luck!!