luff length asym spinaker vs torsion line length

[waltdownunder]

I would just like to check if my thinking is right, if I may.
I have a Facnor FX2500-asym furler from a previous boat. This is the type with a “pick-up line” about halfway the luff of the sail to start the furling in, as opposed to the top-down furlers which are now more common. The FX2500-asym has swivels for the head and tack attachments, so the torsion line turns completely freely. I now want to use the furler for my current boat, which came with an asym spinnaker (with sock) when I bought the boat, a Beneteau Oceanis 350. I have already changed the torsion line length for the new boat. I'm using a small bowsprit.
Now, when using a furler with torsion line, the distance between head and tack is fixed and is determined by the length of the torsion line, correct? Some adjustment is possible by varying the sail attachments to the top and bottom of the furler, but not during sailing. Therefore it is important to make sure that the head-tack distance is the most optimal for that sail under most common sailing conditions. This is a disadvantage of using a torsion line furler instead of a free flying sail hoisted directly with the halyard.
I was looking for information regarding recommended luff length vs torsion line length but does this really matter at all? As long as the distance between the (existing) asym spinaker or genaker attachment points on the furler swivels is the same as the head-tack distance for which the sail is designed, the pick up line will pull the luff to the torsion line and furling in of the whole sail follows. Have I missed anything important?