Blur postprocess different on iPadMini and iPadAir

Hi, I am using the "FastBlur" post process shader from the Pro Image Effects pack. However I have noticed that when I run on iPad air it matches my PC and OSX builds perfectly but on the iPad Mini the blur shader causes everything to get much brighter. I have isolated it to this shader by running no other effects. from looking over the shader code it seems to be doing a standard gaussian blur so I'm thinking it may be a precision issue with the weights adding up above 100%? Has anyone else seen this issue before and is there a known workaround to get consistency on iOS? Thanks Adam