What DPI is your Windows set on? Most likely the dialog is not resizing with the DPI change. WinForms never really does that properly anyways, so that's a mixed bag. WPF matches DPI perfectly, but WinForms just throws up when you change the DPI in Windows. It could also be a problem with the form resizing because it doesn't need to show the Domain text box.
That is the LoginForm in the MicroFour StrataFrame Security project if you want to modify it yourself. The best thing to do would actually be to implement the ILoginForm interface on your own form. That way you can put your own logo, app name, etc on it. The LoginForm is just the generic one that we put in there, but implementing ILoginForm is the best practice.