John, you can get the back end of the cutter to come up off the ground more by using the middle position on the back of the tractor for connecting the toplink to the tractor, instead of the top position, as shown in your first picture.
But that does not solve the other issue of why your toplink is fully extended and there's no "slack" to allow the cutter to move over minor hills and dips as you mow.
Looking at several images of Landpride RCR cutters online, it appears to me that the "A brace" Dave mentioned (the bracket assembly where the toplink from the tractor connects to the mower), does lean back from vertical in many of the photos... that must be the way they are designed by Landpride, and it's a bit unique, I think. Most of the cutters I've seen have that "A brace" standing straight vertical, not leaning back slightly toward the rear wheel.
That's not a major deal, but it does mean there's several inches more toplink length needed in order to get that U-shaped bracket to drop slightly while mowing (the "slack"), so the deck will follow the contour of the field. I think a longer toplink would solve the problem. Not too expensive at places like Tractor Supply.