RE: Am I right about the mast foot position all the way back on an F-type?
I think you would be seriously overfinned.
There's a ratio/relationship between board width, tail width,
and fin span.
If you go too big, you might get planing early, but you won't be planing fast, and control issues will "appear" before the board can get up to full speed.
If the wind stays < 12, a super big fin can work, but once you get the board fully lit up, the drag of the big fin will slow you down, and at some point will become hard to control.
I sailed the Apollo this evening with a 39 cm Tangent Dynamics weed fin, and I was able to plane in about 10-11 knots with the 7.5 Severne Glide, but a 39 cm fin on a board with a tailwidth of almost 100 cm makes for some serious control issues.
So, the board width/tailwidth/fin span equation works both ways.
Too much fin span is not good, and too little fin span is also not good.
I didn't spin out, but found it difficult to keep the Apollo from wanting to head upwind, (lots of front foot pressure and unraking the rig required to bear off at all).
But, when sailing in the Pamlico Sound, over the 40 cm deep sandbars,
you have to use a fin that isn't going to drag on the bottom or you'll get "pitched" violently over the front. Been there, done that.
In summary, the 75 cm Apollo fin would be too large for the F-Type 158
I found the stock fin was pretty good on the F-Types, and I would use Deboichet Concepts up to around 66 cm on that board.
Hope this helps,