Ahahaha! A little conceit of mine. I've written a MonoBehaviour you can add to simple objects to allow them to attach to other things like the car body. I'll post it all on a Git Repo when I'm happy with the code. Ofc, you could always decompile it if you can't wait.
Hahaha! I thought the picture would be a clue but I'll help you out...
Grab the base of the aerial and go to the passenger side wing. The fixing point is near to the corner of the bonnet. Watch out though, the aerial is rather twangy!
It should work out around 90cm. I took a look at some after market aerials and that length seemed a good average. I think it highlights how small the Satsuma is!