the last three corners I have to work on will all be less than 3". the molding I've been working w/ is 3".
due to the irregularities of the post, I can think of two options.
1. get the molding ripped (will depot rip molding?) to the widest width i need and use a belt sander to get a good fit.
2. cut the molding with a jigsaw and sand to fit.
The gap gradually widens to about 3/4" as you go down.
On another corner I had a similar gap that was initially wider. I actually fit another 2 X 4 in it. I then caulked the remaining gap, which still widened to about 1/2" . I put some rigid foam insulation in the gap and caulked. It was messy to do, but it now looks clean. I still want to do something with the existing space.