Guys,

It doesn't help to understand if something's changed in spi design to speak of tight luff or a loose luff.
Please let's stick to the numbers.
Please Rolf take the time to measure the luff of yr Gransegel asymmetric.
Are you sure about the 9,10 mm distance between max hoist and end of pole?
Apparently it seems to me a little too much.
Please follow my argument:
since the max hoist is set at 8,18, we can estimate the distance between max hoist and pole attachment to the main beam at 8,30 m. Now square root of (8,30x8,30+4,00x4,00)= 9,21 m with the pole parallel to the ground.

Please Dan and Tornado Alive do the same (i.e. take the measurements) on yr F18s.
The distance between max hoist and pole attachment in F18 catamarans is very close the Tornado's (as per the F18 class rule max hoist is set at 8,15 m), however the pole lenght should be a little less.
From the examination of the pics F18 spi apparently have a shorter luff but I would not trust much into pics.
Please check also the girth of yr F18 spis.
Thanks

P.S.
Incidentally are you aware of Gransegel spis on the boats of WORLD CLASS F18 crews?