Image-based shader Ztest issue

Hello, I am in the process of writing an image-based shader requiring two different z-passes. - one with Ztest LEqual - one with Ztest Greater However, in all cases, I get a Ztest LEqual buffer. I am using Unity Pro, and I get an almost satisfactory result when I use the Ztest Greater on a material, but it never works on image-based shader. Is there something obvious I am missing?

Also, I know there is a builtin shaderlab variable that stores the offset to convert UV coordinates to screen pixel coordinates. Does anyone know its name?