You might find some info here:
I put these blocks on all my singles, heavy or not. The bees relish them. Even if they don't need them, it sure makes me feel better, in the dead of winter, knowing the blocks are easily accessable.
(Feeder in the hive is empty-just left in to take up space. This is a January 2014 photo)
I just flip over my screened inner cover to use the deeper side to accomodate the sugar block.
There is no substitute for fall feeding of syrup and protein.
I offer the fortified sugar blocks as an additional free choice feed suppliment source for the bees. What I find is they keep more of their honey for brood rearing in spring. I also find it seems to support contentment during the winter months.
Whether they treat the sugar block as a glass of fine wine or an MRE depends on how well you prepared that hive late summer/early fall.