I have four monitors. All apps are opening where I want them to, except Thunderbird.

I want Thunderbird to open across monitor 3 and part of monitor 4. I'm trying to use 'save window positions', but it seems to remember the position only until I close an app, then it forgets where it was.

For example, I'll
open task manager, Word, and Thunderbird.
do 'save window position'.
move them all up an inch.
do 'restore window positions from last save'
All windows go back to where they were when saved (as expected, all good)

But! If I
close the three apps
open the three apps
move them up an inch
the restore does nothing

Do I have to save the window positions as a profile or something?

I really just want to control window the size and position of Thunderbird because it won't open across two monitors, like I want it to, by itself.

How can I make Thunderbird open in monitor 3 and overlap about halfway onto monitor 4?

thank you