You are getting what I want to do!

It is very cool that one can do an area render over your previous render, but the area render leaves a whitish mark on the bottom and right hand side.

I just noticed that there is a "render over black" option in the render settings. I don't know if that would work for area renders but I am going to try it now.

Poser 11 Pro, Windows 10

Auxiliary Apps: Blender 2.79, Vue Complete 2016, Genetica 4 Pro, Gliftex 11 Pro, CorelDraw Suite X6, Comic Life 2, Project Dogwaffle Howler 8, Stitch Witch