Sorry for the lack of a close up pic. There are a series of holes along the bottom of the mast holder, and the top is adjustable by lengthening or shortening the all-thread. I made this for a class 5 sized rig, and I'm able to change rake, and move the mast fore/aft depending on the size of the sail.

These are old pics, but I also lowered the tab on the mast support to a lower point (second pic), keeping the all-thread closer to level with the ground.
The last two pics are a similar setup on a big fat tired mini... Just for stimulating your imagination.