I'd be surprised if
Regulation (EU) No 531/2012 wouldn't apply to small parts of the Swiss networks' coverage area. For example, are the Swiss networks responsible for providing mobile coverage in
Büsingen (Germany) and
Campione d'Italia? The latter is part of the Ticino +41 91 area code despite being in Italy. Given that the home networks can't distinguish between roaming in Switzerland and these small parts of the European Union, I imagine they would have to apply the price caps to all roaming on Swiss networks.