Bees feed from the bottom up, so by the time that they need the fondant the bees will have eaten through the stores in the brood chamber and the shallow on top so should be clustered just underneath the crown board - so the fondant, in a tub over the feed hole, will be conveniently near.
Bees will store fondant just as readily as syrup - given the right conditions
In the autumn or balmy spring when they are able to fly to get water, they will dilute the fondant down to sugar syrup consistency and store it as 'honey' (when people are convinced that bees store fondant 'as is' packed into cells, what they are actually seeing is white mould on pollen)
I have witnessed bees, in the autumn, in a hive virtually devoid of stores, take the best part of a 12.5 kilo slab of fondant in less than a month, when subsequently hefted, the hive was nailed down and didn't require any supplementary feeding at all during the winter or early spring
In the midst of winter when bees are clustered and reluctant to fly they will just use the condensation present in each and every hive to dilute the fondant just enough to eat, therefore use it as a ready food supply rather than store it.