One question about your candy recipe and method. When you pour the syrup into thre frame w/ screen, how thick does your candy become?
It becomes pretty hard, depending on what temperature you cook it to. I usually get it somewhere between the hardness of a pressed salt lick and rock candy. I usually get impatient cooking and it ends up on the softer side. The softer it is seems like the more likely it is to crack when it takes on moisture. That is why the hardware cloth is nice. Once I pour it and it hardens, I don't care if it cracks and breaks away from the wood, because the hardware cloth keeps the chunks from falling down into the hive. One thing I have noticed is that the bees seem to eat the edges first (speculating that is where the condensation forms) and this reduces the area "holding" onto the wood and then it is more likely to break away from the wood.
secondly, what temp is candy when you pour?
I try to get it around 260F.
Another thing I have found to work fairly well on hives that are marginal on stores and depending on how tough the winter turns out, is to feed the candy above the inner cover.
At first I made the candy in loaf pans, but then found 9x9 foil pans for like 3 for $1 that are even better (no more getting the wife upset about sticky loaf pans). I run inner covers with 2 holes like this:
I then just lay the candy block over the holes once the bees work their way to the top.
There are some pictures here:http://robo.hydroville.com/v12/content/view/23/2/
These were from the loaf pan days, and that particular one looks to be the last pan in a batch and the sugar had started to cool down and harden when I was pouring.(hence the rough looking top).
The nice part about this is you can do it in the Spring to just those hives that need it, and you don't have to open them up and get them chilled to feed them.