It is possible to split the workspace (the area for the document windows) into two halves and have 1 or more files on a file tab on left side and 1 or more files on a file tab on right side whereby on each side only 1 document window is shown maximized as it can be seen at top of attached image.
It is possible to split the workspace into multiple parts each which is own file tabs bar and with 1 or more files on each workspace part whereby on each workspace part only 1 document window is shown maximized, see middle of attached image.
And with right clicking on any file tab to open its context menu, opening submenu File tabs and left clicking on first item Dockable to toggle from not dockable to dockable file tabs/document windows, it is possible to completely free arrange all the document windows in workspace area with all files having a common file tabs bar, see bottom of attached image. It is possible with Dockable file tabs to hide the file tabs bar completely to get more vertical space as each document window has a title bar showing the file name.
But a workspace splitting plus document window arrangement within each workspace part as you would like is not possible because the Microsoft ribbon framework used by UltraEdit does not support it. It is not possible to split workspace area into two halves each with its files on a file tab and additionally arrange the document windows inside a half of the workspace side by side.
Best regards from an UC/UE/UES for Windows user from Austria