I have been a Fences user for some time. Today at work we got a Samsung 49"double width monitor for a customer, and I was testing that. Works great, but it is still one monitor. in a double monitor setup you can make use of the Windows "snap to edge" functions for getting your windows aligned into 4 side-by-side windows. In case of the ultra wide Samsung, you only have 2 side edges, so you can set only 2 windows side-by-side. That is a disadvantage of an ultrawide monitor I guess.
Maybe it would be a great idea to have a feature in Fences or one of the other (or a separate!) apps, to enable "snap-to edge" in multiple columns, by dividing the upper edge into segments. Pressing the windows to an edge segment aligns the window to the column that segment represents.