Hi Jeff,
I think this is the result in the area you are talking about:



I only did the one side but this should show you what to do...

What you need to do is to create a copy of the piece that you want there and do a "boolean difference" with the copy.. Then you can boolean add the piece in to acheive the variable...

Note: When i did the boolean difference, I zoomed into the area and deleted a little fragment that was left over to clean it up a bit...

I've included a file with just the piece there in it to be sure we are talking about the same thing..