How do I keep my lightmap uv's unchages so that modular pieces can have the exact same pixel density (as per the lightmaps that I made)?

Unity seems to change the scale of the lightmap based on how big the objects are. But that's messing with the perfectly sized lightmap uv's I made. T$$anonymous$$s means that I'll get seams if I place modular pieces next to each other that have different lightmap resolutions. Is there a way to get unity to just use what I gave it without changes? Or is there another way to ensure that my modular pieces have the same lightmap resolution?

Here's the meshes with their uv's http://imgur.com/Ah0AfIl,HP6mmiO

But as you can see the bottom piece are smaller in the lightmap than it should be http://imgur.com/Ah0AfIl,HP6mmiO#1

I'm really hoping someone can tell me what I'm missing here