Special Window settings for Thunderbird

Trying to setup special window settings for Thunderbird, and not having a lot of success.
Just trying to setup the initial window, on opening Thunderbird (which has the title “Inbox - - Mozilla Thunderbird”), to sit in a particular spot, and for the window to be a particular size.
I open the special windows settings, with Thunderbird being in the correct spot, and the correct size, and add the position and size, but need to also add something to identify the PARTICULAR window.
So, I click on the Detect Window Properties button, add Size and Postion, but then am confused as to how to actually add the Window, itself.
If I just do a Window class, Exact match for “thunderbird-bin thunderbird-esr”, it works perfectly (initially…), but any dialogues/incoming mail boxes/ANY Thunderbird window, then comes up with the exact same position/dimension…
Anyone have any idea on how to restrict the settings to only the MAIN window?
Thanks.