A lot of water has gone under the bridge since I posted. I had given up hope. Here is some more information. I don't have a pic handy with the door open.
black: soft weatherstrip of the threshold
gold: metal part of threshold
brown:added wood under the threshold that I though was flooring
Gray: Recently-painted riginal door sill if "sill" is the right word
Mottled gray-green: concrete porch deck that I have not yet had time to paint.
I do have a wider shot if that helps.
I learned that the wood visible between the metal of the threshold and the gray sill is not flooring, but plywood. They expect to caulk it. It is nearly flush with the edge of the threshold.
Unfortunately, the sill does not slope much, if at all. I wonder if a new sill should have been installed. There is no gap between the threshold and door. The door had to be cut to make room for the new threshold. Note that the subfloor (plank) was replaced with plywood and brought up a little to match up with flooring in the rest of the house. This must have resulted in the need to raise the threshold with the added wood on top of the sill.
Thanks for responding.