Currently, we only get one panel per block. As I understand it, it's because panels are based on trapdoors. Still, while they have the trapdoor attributes: top, bottom, open, etc., they are not trapdoors. Because they are 1/4 of a block thick, it would make sense that you would get 4 panels per block. If you want to account for waste in manufacturing them, 3 panels per block. Otherwise, they become fairly expensive as compared to slabs, which are 2 per block.

Do panels work like Applied Energistics 2's cable facade?https://appliedenergistics.github.io/features/decorative-blocks/cable-facade

Do panels work like Applied Energistics 2's cable facade?https://appliedenergistics.github.io/features/decorative-blocks/cable-facade

No, but that is beside the discussion of this issue, this is related to the recipe of creating these panels in the first place.

Speaking of which, that has already been implemented. You now get 4 panels per block

Oh sorry, I misinterpreted the OP's statement.