Question about Dual Graphics and memory.

I apologize if this is documented somewhere, but I haven't seen my exact question here or elsewhere.

According to my event viewer, when it notes a performance problem, 99 times out of 100 its "video memory resources are over-utilized".

My understanding of the way integrated graphics works is that it will make use of RAM to make up for running out of VRAM (or is it that there is no dedicated VRAM, and what's reported is just the allotted shared memory?).

My understanding of the way Dual Graphics works is that VRAM use is bottlenecked to the lowest source of VRAM in the connection, that is, a 4gb card and a 2gb card together can only use 2gb vram.

My question is if I have an integrated graphics board and a discrete card with Dual Graphics enabled, what's the memory situation? Is shared memory still a factor even though there's a discrete card involved? Does the Dual Graphics memory bottleneck mean that the RAM used by the APU can't go over the GPU's VRAM (and vice versa), do the APU and GPU work in tandem utilizing RAM as shared memory, or is it that shared memory can't be used at all with Dual Graphics?

Ultimately, I suppose the issue is that if my performance problems are foremost a video memory issue, can it be improved with more RAM and increasing what portion of that is shared memory?