OK...today I removed the seat back rest, and as Chuckie suggested, it made a substantial difference !
It was obvious when seeing the underneath that my ideas about relocating this back rest would not work. It had to go.
I rode around town, and the seating position seemed a little lower, and farther back/relaxed. I pushed my butt all the way back, and my feet seemed to stretch out more, when I lifted them into "normal"
[ 45 degree ?] road position.
When I came home, I took the seat back rest and reinserted it withour the nuts/washers, and took some measurements:
Seating position with feet flat on floorboard, butt all the way back, toes to front, front wheel straight, hands on grips:
Distance from Knee to "caution" word on caution label......with backrest: 6 ", w/o backrest: 7-1/2 "
Distance from navel to Yamaha symbol in the middle of handlebars: ...with backrest: 18", w/o backrest: 20 1/2"
So, this does make quite a difference for us tall types ! Looking forward to trying this on a road ride...50-100mi. There is no foam padding in the back of the seat curve, but this did not seem to be uncomfortable initially. But I've got a few ideas...read on...
Now, there is the issue of the holes...4 open die-cut 1/2" holes in the rear of the seat. First, a piece of thinner foam could be fastened on the outside, or pushed inside, if a couple of staples were removed underneath. The foam could be black, of a piece of vinyl fabric could be wrapped around the foam before gluing, bolting, or velcroing it on.
Another solution is the "Butt Buffer" pad www.buttbuffer.com
that I have coming...this may lay over the holes just slick as anything, and be velcroed if necessary.
So far, a great improvement for almost no cost...thanks, Chuckie !!