there's hardly a street in san an where you can't park. some parking is free, some is charged and for a limited time. here's my tip, always make sure your bumpers are touching at least one of the cars front or rear, both if possible.
Make sure you get a ticket if your in a bay with blue around it, saw many a car getting ticketed last week for not having one.
the orvay on calle de fomentara is in ibiza town is it not?
I guess you mean formentara 2?, which is not far from calo des moro beach, there is many a good parking places around there, there is some open ground not far from where you are staying next to the fruit stalls off the main road (across from Davids pizzeria), there are always spaces there and they are free too.