Mine are the same & I had the same concerns as you. However, after 6k miles they are still ok. I tried putting an extra O ring on them to improve the fit, but it made no difference.Just fitted the H11 switchback fogs from Autobeam to my van and I am a bit concerned over how loose they are when installed. So much so that I am not only worried that they might allow moisture in, but also that they might actually vibrate out over time.
I have given them the benefit of doubt and left them installed for now, but will be keeping a close eye on them.
Is this a common problem? Is there a way around it? Can the bayonet tabs be bent a bit to make the fit tighter?