Quote:
| They are far enough apart |
I'm affraid you don't really know much about the cooling assembly within the XPS2.
Allow me to teach you

There are 2 heatpipes with radiator blocks for the GPU (1 on the left and 1 on the right side of the chassis) and 1 for the CPU.
The 'left' one is co-located directly behind the radiator of the CPU and they both use the same cooling airflow.
The air thus cools the CPU radiator first and only then the GPU radiator.
A stupid order, but perhaps made so due to technical constraints.
A hotter CPU means the air leaving the CPU radiator will be warmer too and will be less effective in cooling the GPU radiator thus increasing the GPU temp.
Mind you, my own tests with undervolting/clocking the CPU didn't exactly drop the GPU temp by any huge ammount, but it could make a difference and the principle is sound.