Really doesn't matter. You just need to have at least 1 card that is large enough and able to load the dag alone. I have 6 rigs this is functioning on, all were 6x Rx470 4GB rigs, but then I took out a card in each and replaced each slot with an Rx580 8GB once I discovered the fix. Distributed the set ups so every 4GB rig has at least one 8GB card to load the dag. I have not confirmed if an Nvidia card can assist another Nvidia card in this way, I don't any under 8GB however the even stranger thing about all of this is that a p104-100 8GB will assist my Rx470 4GBs and they will mine.
You will need at least 1 GPU to load the DAG plus the Windows data system files on the GDDR. But you will still need to have at least 4GB for the other GPUs. What I mean is that you can't have 1 GPU that has 8GB GDDR and have the rest being 3GB GDDR GPUs. It won't work I tried.
The way the Claymore software works is that it needs to load the entire DAG onto each and every GPU. It doesn't just load it only on the first GPU. You can look at the resource history monitor and you will see that the memory for each GPU is completely used up. So this will still only work with any GPUs greater than 4GB but anything 3GB or less is obsolete in mining ETH right now.
What cards are you testing? This may not work for Nvidia 3Gbs as I stated I only got it to work with a Nvidia p104 assisting a Rx470 4Gba.
The way I discovered this fix was half my farm, about 6 rigs with all 4Gb cards, went down and stopped generating the dag on both eth and etc. I realized that one of my mixed rigs with a 8gb worked fine. I tested it by removing the 8Gb. All of sudden it didn't mine. I tested this on the other rigs by dismantling a 580 8Gb rig and distributing the cards to each of the 470 rigs. This works flawlessly.
As for my r7 200 series I have a desktop build running in Windows 10 legacy mode. That build I can install my 580 8Gb or other Polaris cards with enough memory for dag, and sit the R7 200 next to it. The dag loads perfectly fine and mines. Takes about 57 seconds to load the dag and mines at a pitiful 1.2Mhs.
I noticed this a few years back as I mentioned but now with the dag approaching some cards thresholds again and clearly mine, I rehashed this. (pun intended)
Legacy and UEFI mode have alot to do with how pcie slots will interact with you cpu and motherboards chipset. UEFI is going to give you the latest pcie options and most lanes. Legacy is a much older way of installing Windows and restricts pcie lanes available and other features included in the bios and operating system.
