Dont recommend multi GPU as Multiprocess is more efficient and you are going down that path anyway. Some of what you are describing splitting the frustum and rendering separately is more a 2110 config. You dont refer to being in a 2110 setup so it may ust be the terminology, which to be fair can get confusing. I would take a look at this link Converting a mGPU config to Multiprocess rendering You are not converting but the end result config is very similar to what you are trying to do. The final result has the wall split in two and the ceiling split in two and two wild wallls. Note the settings that need to go from SLI enabled to using mosaic in Multi process. If still stuck. Send a link to where I can download an empty project that includes your current nDisplay setup in a generic version of UE from the launcher and I will take a look.
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