For what it is worth sabydent, I think you should drop the mast back to where it was and put an extension on the TOP of the mast with enough length to be able to adjust sail height.
Your mast looks to be flexing rearwards way to much which will change the dynamic of the Centre of Effort in relation to the Centre of Lateral Resistance.
The raised height of the sail increases the lever length between the Centre of Gravity and Centre of Effort as well which causes the yacht to tip over more easily.
As suggested, tilting the seat back further back to about 30 degrees will give you more head clearance under the boom and a greater sheeting range.
From the looks of it that sail in my opinion is a good high wind sail and I would leave it alone for the moment.
Were I you, which I am not, but if I was, I would be working on getting a fairly stiff but taller mast and a larger area sail with a higher aspect ratio, ie taller in comparison to the base length or in sailing terms more luff in comparison to foot.
Don't you just luff this sailing caper.

Edit:- Here is a plan for a "stiff" aluminium mast that Paul put up some time ago. It was the first mast I sailed my Mini with and it went like a rocket. He took it home with him and I had to build a sectional mast from a couple of windsurfer masts which while good, does not deliver the power to the yacht as well as the ally mast.
Edit 2:- If you can end up with something like this combination of mast and sail I think you will be very pleased. Just scroll to one of his posts, click on his profile and then on the right, click on his photos and you will find a lot of good stuff.