Thanks guys!
I'll definitely try the 80/85% rule using a drinking straw - that would make the fuz about 10" long - quite a lot longer than now. I'll report back on results.
Tim, the mod is just a bog standard 'take off the bottom wings and stick them on the end of the top ones with tape' mod - I did chamfer them a bit to get the dihedral to be continuous (ie straight line) - as features on page one of this here, now officially the longest thread in the history of blogging, possibly!
Cheers
Ayrton
ps why do Skodas have heated rear windows?