Hi Anthony,
Thanks for the idea of switching the holes in the lower body tension cap (part 812/A in the diagram). As you can see in my post, giving the cage one 360 degree spin counterclockwise, gives me really tight tension. I'm thinking that maybe I can switch holes like you've suggested. Also it might be that the chain is a link too short.
With the chain on the largest chainwheel and on the largest rear cog, the dérailleur is almost in a horizontal position. It's probably streched too much and what with the high tension of the lower body spring pulling on the cage and what I suspect is too short a chain, maybe there's something to invesigate.
I'll keep you posted,
Jack
P.S. Thanks for taking the time with your Photoshop drawing tool, too!