...I had someone saying to me once my setup was wrong the way it is but I'm happy with 48 degs on the cards.
I also once had my top GPU using the 45° angle fitting from the CPU and nothing was said and all was well. Otherwise how else do you go from the CPU to the GPU (using about 10cms of 1/2 ID tubing) that close without kinking.
From years of doing loops I normally go left GPU inlet port for single cards and dual parallel otherwise top right for dual serial. I'm no expert and simply follow the instructions based on the setup
For dual socket you could have went dual loop route, normally only a consideration if with multiple GPUs the temps are high. Your case already looks tight and not really possible, ie cases with removable drive cages to fit dual rads.
When you use parallel the coolant flows through all GPU blocks together, diagram below. If all goes to plan I plan to use the top left inlet then come back out the top right using optional G1/4 extender. Using the normal bottom right outlet not an option as bottom rad inlet is on the left (other side near rear of case).
Out of curiosity, what is your CPU/GPU temps? Will let you know mine in due course, probably late next week with delivery being 3 days.