Welcome to the forum!
Do I understand that you've somehow hacked Inkscape, so that the docking area is separated from the main window? Or do you mean that you keep the Inkscape window sort of halfway on one monitor and half on another? Or by "floating dock" do you mean that you're using floating dialogs, and you place them all on the other monitor?
If you've hacked on Inkscape, I'm not sure if you could expect those windows settings to still work. Not unless you really, really know what you're doing. In this case, you would need to consult developers. I don't know if they could help. But I know we probably can't help (as a user forum).
(Or if you do really, really know what you're doing, perhaps developers would be interested to see what you've done. Because that looks like it would be a really nice feature!)
If you're keeping Inkscape part on one monitor and part on the other, or you're using floating dialogs, I would expect the window behavior settings to still work. But with a big "However" that there appears to be some kind of bug or bugs when using Inkscape on multiple monitors, where dialogs seem to disappear (really they are just getting lost outside the screen area) or the dialogs just don't stay put.
You could try digging up those bug reports. Maybe some workaround or even a fix has happened, since the last time I saw them? I would try searching "dual monitor" or "monitor" or "multiple monitor" or something like that. For Launchpad, it seems the fewer search words you use, the better. It's not the kind of search where you can type in a whole question.
https://launchpad.net/inkscape Or there's another relatively recent message in this forum about dual monitors, where I remember searching out bug reports. It would probably be easier to search the forum, to be honest
(Although the title of the message might be something about missing dialogs, eventually the subject turned to the dual monitor.)
Edit
To contact developers, best would be the development mailing list (
https://inkscape.org/community/mailing-lists/) but there's also a development IRC (
https://inkscape.org/community/discussion/)