Custom model not always rendering bottom texture

I've made a custom table model for a block in Blockbench, and for the most part successfully implemented it. However, if (and only if) there is a block below the table, its bottom texture will not render. I presume this is how solid blocks work since they are fully covered, but in this case the lack of rendering is fairly obvious from certain angles. I've tried changing the texture transparency type and none of the options change anything. Is there a way to make sure the bottom renders in all cases?

Here's a demonstration screenshot - the table to the left is in the air and renders fine, but the one on the right on top of a block is borked: