Exactly. That's why they would have to treat all roaming on Swiss networks as subject to the price caps.

I guess both Campione and Büsingen are so small, that they can be covered by antennas physically in Switzerland. As such, if you use these networks, you´re still officially roaming, and tariff-wise/legally you´re in Switzerland, not Italy respectively Germany.

Just as if you´re roaming in a foreign network, just because you´re close to the border. That´s the user´s own fault.

I seem to remember that there was a lawsuit ~10 years ago where a technicaly unsavvy lady visited Rügen/Germany, and her phone logged into a Polish network. She then faced huge roaming-charges, refused to pay and sued. The court declared the charges void, as the pricelist mentioned "calls from Germany" which applied in her case. However, checking today's pricelists, most still mention "prices from Germany" and not "calls while in the German network".

This is the question. If Swiss transmitters are physically on Italian or German territory, then the price caps should apply when using those transmitters. Given that it would be hard for a home network to distinguish between roaming on these transmitters and transmitters in Switzerland, they would have to apply the price caps to roaming on Swiss networks anywhere.