Last night (5th night out) all but one had gone into the coop on their own. Tonight, everyone was inside when I went out to check. Less than a week and training is complete!
Now, to your issue
jaydweight. That ramp does look awfully long. On the other hand, I wouldn't want it to be any steeper.
That said, I do think that is the issue. It's very high off the ground from a chicken's standpoint. Here's what mine looks like (sorry I don't have any closeups) - it's 3 feet long but the angle may be a little steeper than yours.
Unfortunately, I don't have an easy answer for you.
BTW, your coop is very nice - I wouldn't call it ghetto, I would call it a clever use of limited resources.
falinagirl I did the crawl with my first batch last year and ended up with a backache, too!
This year I got smart and blocked off the under coop area for the training period.