Pls see my new grid for the most simple split and span functions over two monitors. And it works fine with one monitor at command 2 50% left, command 3 50% right and command 4 100% full screen.

The attached grid allows for layouts like

UNDO monitor 1 = WIN+G+1 and UNDO monitor 2 = WIN+G+2

50/50 split full height for monitor 1 and 2 ( WIN+G+3 | +4 | +5 | +6 )

|--------|--------|  |--------|--------|
|        |        |  |        |        |
|        |        |  |        |        |
|        |        |  |        |        |
|--------|--------|  |--------|--------|


100% per monitor 1 and 2 (WIN+G+7 | +8)

|-----------------|  |-----------------|
|                 |  |                 |
|                 |  |                 |
|                 |  |                 |
|-----------------|  |-----------------|



span over two monitors (WIN+G+9)

|-----------------|  |-----------------|
|                                      |
|                                      |
|                                      |
|-----------------|  |-----------------|