Shield texture compression

I've been working on a mod that adds several new shield variants for minecraft and ran into an issue while trying to make taller shields. When i was making shields they used their 3D models when lowered but used their Texture (as in icon) as their raised model, this worked fine before when i was making smaller shield like roundshields and bucklers but, as said earlier, has become a problem with taller shields. The taller shield texture doesn't use it full size and insteads opps to keep its parameters in the 16:16 ratio of normal minecraft textures and therefore compresses the texture and makes it smaller. Is there any other element i should be using instead of just the normal "Tool" or is there any way to fix this.