Multi PSU & GPU setup help!

Here's my setup so far:

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[EVGA 1200w PSU1]
MSI Pro Z890-P WIFI
Intel Core Ultra 9 285k
96Gb RAM
RTX 4090 - PCIe slot 1 on risers

[Corsair 650w PSU2]
RTX 3090 - PCIe slot 2 on risers <--- question here 

PSU connected with a ADD2PSU
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I'm hearing conflicting recommendations: 

1. I should cover the 12v pins on the riser to the 3090, sicne the motherboard uses PSU1.
> Non-Powered Risers (Simple Ribbon cables): These purely "extend" the connection. If you use one of these to connect a GPU to PSU #2 while the motherboard is on PSU #1, the GPU will try to pull 75W of 12V power from the motherboard (PSU #1) while pulling the rest from PSU #2. This "cross-talk" between different 12V rails can cause instability, power back-feeding, or hardware failure. This is where people recommend the "tape mod" to block those 12V pins.

2. The counter to that is that GPUs (3090) expect the extra 75w of power from the riser/motherboard so I should never cover the 12v pins.

Any advice would be greatly appricated before I blow up my setup!