We are experiencing this same problem, most problematically with a new user with a vision impairment. At display settings they can effectively use for day to day work, their monitor does not offer enough height to show the buttons and controls at the bottom of the dialog.
Could perhaps the dialog render a scroll bar if the window height is not large enough? Or perhaps allow the size for the tabbed widget (Description, Participants, etc.) to go smaller, as it seems to have a rather large minimum height?
The solution they are using, which is a source of annoyance for them, is to temporarily zoom out to get to the buttons, but then they need to kind of remember the text on those buttons because of the aforementioned vision issues.
