Here's some idea ss22,
Thanks to Lienart for picking up on pen layout. I did some rough beer coaster measurements, and the angles to the posts is a bit ordinary if its for a 10mtr berth. But if you:
a) cross your stern lines to the opposing posts, this creates more of an angle and looks good enough to hold your stern from wandering in a cross breeze; or

b) make a bridle for the stern lines that fit off to the posts. This cheats by adding a virtual 'length' to the boat but would be a bit more work in rigging and in tying up.

Some ideas at least, cheers,
SB