Don't the diesels use a different servo assist system as you don't get the same vacuum when you lift off as you do with a petrol engine? Every diesel golf I have driven, including my sons Mk6 GTD has a softer pedal.
Remember, you are asking the same size master cylinder to move a bigger brake caliper, so that may be part of the problem as well.
Another thing to try is just lightly tap the pedal, almost as if you were flashing the brake lights and then immediately brake hard. I'm sure its something to do with brake assist, but if I do that on my gti, the pedal always feels firmer.
On the other hand, I could be talking out of my backside, it has been known.. (well apart from the last para, that deffo works!)
