Is the cup spoiler of a 172 the same as the cup spoiler of a 182?
I've got a 182 with both cup packs, and the standard aerial made the tiniest amount of contact with the spoiler - not enough to be worried about. I took a hacksaw to the aerial anyway (and replaced the rubber cap on the end) as I think it looks better shorter. I wanted to fit one of those really short, stubby, 'bullet' style aluminium aerials (anodised black) - but figured it would get pinched. Radio still seems to work fine, but I mainly listen to cd's anyway.
Iirc only the V6 and Trophy specs. needed shorter struts - because they have the largest spoiler.