I just got around to installing my set. The aforementioned gap is huge on my car (the tabs are barely engaged) and the locking tab itself on the part does not engage. They fall out as soon as I stop holding them in and I do not want to trust the top cap to hold them in. Back in the box they go. I don't feel up to modifying them to get them to work. They do look really nice and well made, it is unfortunate that they just are not shaped properly.
My son has a set he installed, I will look at his and see how much gap he has. He is much less picky than I am about this sort of thing.