Hi Mark,
I think that besides keeping its aspect ratio, a triangular sail keeps its centre of effort forward when reefed. When we reef our junk sails deeply, CE moves aft and, on our schooner, we have to take more out of the main than the fore. We live with it.
Your point about fractional versus masthead jib might be quite right, assuming there's no mast-bending system at work.
The Aerojunk has many possible planforms, from imitations of standard shapes, to the downright fanciful!
The split junk (almost typed 'spilt junk') rig seems a close relative. Aerojunks have an intriguing future, if Paul MacKay and others are able to put the development effort into it, as Slieve has done for the split junk.
Cheers,
Kurt