In the interests of economizing space I've further modified my set-up, much like Marvin, and the "legs" are gone. The assembly is now clamped to my easel as well. (I've resigned myself to canvas widths that "fit between" for now.)
On the right end of the horizontal pole you can just make out the loop I attached there. When the angle of the prop becomes too extreme, I just throw the loop over the peg on the high side.
(No more limbo fests I'm afraid, Tim.
)
Regards,
Dave