I think I understand what you are trying to achieve, and from the sounds of it, it is a UV scale issue. Each model will have different UV scale and tiling, to correct this you will need to make sure that all of your models have the same UV scale so that the textures will apply universally across each and occupy the same coverage on the mesh. Doing so will make a 32x32 texture (or any size for that matter) apply the same or at least the same size across the models.
I have made several pixel materials 32x32. The plan is to put them on different 3d models, but the size of the texture changes based on the 3d model. It would be nice to make all of the materials have the same pixel size even if they are placed on different models 
for example having the trees and the ground matching in the size when it comes to the pixels in the texture. Please ask questions if you dont get what i mean, would like to solve this 
my material wont apply the texture to a model, i tried to edit the uv with a slider too but it looks like this
on a flat surface it works perfectly fine, but not at the tree is posted