Multi screen setup are common now.
Please allow the main window to stretch down across 2 monitors in landscape mode to display the score in either continuous or paged mode.
Currently Notion 6 only displays on the top OR the bottom monitor OR in between the two with a maximum window size the same size of the single monitor.
Reaper, VLC, Firefox, Musescore even the old program Midiox will all do it.
Both my monitors are the same Acer model at 1920 x 1080 resolution.