I think I've figured out what's going on. So even though I set the width of the form to the device dimensions, with Chrome on Android (or at least this version), if you have any components drawn (even if invisible, and used for modal only) outside the device/window/browser dimensions, it acts as if the window is larger than it's visible components (this applies even if you, at design-time, change the width of the form to the browser window size.
Once I moved all of my invisible controls within the window size, the pop-up ended up center of the window. Looks like this works programmatically moving them in FormCreate too.
Once I moved all of my invisible controls within the window size, the pop-up ended up center of the window. Looks like this works programmatically moving them in FormCreate too.