I communicated with Ronstan and Murrays and tried their ideas of how to solve my problem with getting the lo-profile jib cars to release the sheet when under load.
Ronstan recommended taking the black plate off and flipping it over so the cams would line up better with the roller fairlead. This made it very easy to release the sheet when under load, but difficult to cleat the sheet (since the jib cars are just above the tramp and it was hard to get the sheet low enough to cleat it). This was similiar to when I tried feeding the sheet through a larger eye strap above the roller fairlead.
Murrays recommended flattening the black plate which was a happy medium between the original design and when I flipped the black plate over. With the black plate flattened (see second photo) it works really well now and I can cleat and uncleat the sheet a lot easier now that the roller fairlead and cams are aligned better.
I also tried lowering my jib further down the bridle chainplate so the clew plate was lower and further in front of the jib cars. Being a tall person, I didn't like this since it makes it harder to see under the jib as to what's on my leeward side. Since I sail several times a week around the "Pass" which connects St. Andrews Bay, Grand Lagoon and the Gulf, there is quite a lot of power boat traffic and when sailing solo you can't always depend on power boats to give you the right of way (particularly the pontoon and jetski rentals).
These two photos show my jib control setup (with the flattened plate).

