Mua Cooler Master NR200 Mini-ITX PC Case, 330mm Horizontal Triple ...
large 3-slot GPU on PCIe riser (horizontal) ... Thickness of radiator on front of case + thickness radiator fans + GPU length must equal less than 330mm total.
Can a Motherboard Bottleneck a GPU? - PC Guide 101
Note: Make sure the GPU PCIe Connector is fully inserted into the PCIe Riser Cable Socket and motherboard PCIe slot when powered off.
What is a PCIe Riser? - Linux Hint
A PCIe riser card is made up of a x16 GPU adapter, where the GPU goes in, and a x1 or a x4 GPU adapter that goes into the motherboard’s PCIe slot.