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Yes, I am aware of the fact, that OSE lags behind Google. But I don't see the reason why Google ranks one page higher than the other...

Hi, It sounds like you might need to implement hreflang tags. Have you done so already? Without being able to specify each country-level shop in Search Console via ccTLD, this is your best bet to ensure the right pages show in the right versions of Google. Here's Moz's guide to using hreflang tags. For each of your country-specific subdirectories, you'll need to add the appropriate tag which will specify the country and language of the page. This helps keep Swiss pages out of Google.de, etc, etc.