Due to the use of a big Ventrad for CPU and a big Graphic Card, If i install the Graphic Card on PCIE2 slot, it will block the 2 PCIE 1x Slot (PCIE1 and PCIE3).

The only solution that i see is to put the graphic card on PCIE4.

But the user manual says:
"In single VGA card mode, it is recommended to install a PCI Express
x16 graphics card on PCIE2 slot."

Why? What is the problem to do this?

Thank you very much.