does a well polished and waxed car hinder snow foam dwell?

I gave my car a really good polish and wax a few weeks back, I have washed every week since to keep the winter grime at bay, can tell wax still doing its job as still beading well however I am noticing my foam doesn't seem to dwell for long, get a nice thick coverage, go in the house to sort the bucket out by time I get back out nearly all the foam has ran off, seems to just slowly creep down the panels opposed to sitting on them. Anybody else noticed it?
 
I gathered that, was just wondering if it also makes the foam slide off as I thought snow foam would cling to anything, as they promote their products as wax safe and will dwell for up to 30 minutes etc
 
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