I find it curious that bee space has to be maintained top and sides, but not beneath the frames. I have a half inch beneath my frames. They never build any burr comb in my hives.
Troublesome amounts of bridge comb, burr comb, or cross comb are all rooted in bee space violations. If the space is too small for a bee, they will fill and seal it off with wax and/or propolis. If the space is too large for a bee to reach a leg out and easily navigate, they will fill it in with wax to get it down to her legspan.
In our stacked standard boxes, the frame rest is set for recess of the top bars of the frames, giving 1/2 a bee above the frame bars. The box sides are tall enough so that there is 1/2 a bee space below the bottom bars of the frames. When the boxes stack, you get 1 bee space between the frames inside and no major bridge comb gluing the boxes together. The boxes snap apart cleanly and restack onto another hive with no need for cleanup.
This is another reason why it is important to standardize and to not mix and match equipment from different builders. The dimensions of one builder mixed with those of another builder can result in bee space violations, and thus alot of extra work hiveside cleaning up parts to fit.
My bottom boards have a 3/4in rim. I get some nice manageable bridge comb off the bottom of the frames of 1/2in or so thick which they often fill with drone. Just what I like. The bees do not attach it to the bottom board. They maintain a bee space walking height clearance along the bottom board. Just enough so she can walk in to where she wants, then reach a leg up over her head to grab that bit of bridge comb and climb up the frame.
I do have a few screened bottom boards that the screen is dished down bit, beyond 1in. Those have been horrible for large amounts of bridge comb hanging off the bottom and stuck to the screen. I rarely use those boards for that reason.