Hi Volker,
You seem to misunderstand me. I never implied that modes would have the same resonant frequency for different size patches. I was merely pointing out, from my original post in this thread, that the return loss dips are caused by fundamental modes (and its associated harmonics), and also by whatever feed structure you have.
I was stating that the reason you don't see a maximum gain for all of these dips are that a) As you pointed out, not all modes will be radiating due to current polarities, and b) some of the dips are caused by the feed structure, which will usually never radiate too well.