I'm 10" from the ground to the top of the receiver hole. Unless somebody has a Manley trailer and can give me the second half of the equation, I'll probably just wait and have my friend tow the trailer back to our place from the dock, and get my own measurement at that point.
I'm curious, though... To clarify my earlier response, I did find a great number of height adjustable ball mounts, but every one of them is for a 2" receiver hole, not 1 1/4". I found other message strings on other forums, as well, asking similar questions and the response seems to be that they aren't made for that size receiver hole. I've admittedly done a lot less looking into the 1 1/4"-2" receiver hole adapters (which I thought would allow us to mount one of the height adjustable ball mounts I've found) but those I have seen have indicated they aren't usable for towing applications, just accessory mounts (bike rack etc.)
If you can point me to a height adjustable ball mount for a 1 1/4" receiver hole, I'd be grateful and would happily purchase one! Or, I'll just wait until the trailer is here and I can take a measurement and get the closest matching rise on a fixed ball mount.