I have very strong half-gal. plastic containers with screw lids that I want to use as feeders. I have only two hives, so thinking two per-feeder over the inner cover and a medium over it (fits). I know I will need to raise them up for the bees to get at the holes in the covers of both pails. How high should the shims be(pails raised) for the bees to get at the holes? If too high will they occupy the whole box?