I had a multiple entries schengen-entry Schengen visa issued by germanthe German embassy. My first port of entry by air was switzerlandSwitzerland. I was admitted to enter the schengenSchengen states through that port of entry. I once travelled by road from londonLondon to german by roadGermany.
I had a german schengenGerman Schengen visa too. My first port of entry was franceFrance. I was admitted into the schengenSchengen states through franceFrance without askingbeing asked for my itinerary.
I think at the port of entry they know that with that visa you are allowed to enter the schengenSchengen states so they will not deny you entry simply because you have sought to enter through a state different from the issuing state. All you need do is explain your circumstances.