One normally wouldn't image through the diagonal, you won't be able to get enough infocus.
I know that it's very uncomfortable trying to get to the back of the camera when you're close to zenith but one just has to make the best of it.
One of those plastic backed picnic blankets is better to lie on than a regular tarp.
Invest in a Right Angle Finder for your camera. They're not too dear and you can increase the magnafication on the view 2x if you want to.
Or sell your refractor and buy a newt.
They both have their pro and cons re. comfort, but when I get sick of one I can always swap to the other.