Although you do get these options in the help text (ie. when you do enter gdialog without any option), gdialog doesn't use <height> and <width>. gdialog --yesno hello 10 10 and gdialog --yesno hello 10000 10000 do exactly the same thing.
Gdialog accepts options dialog does so that you can use files without conversion. It doesnt however honour all of them. Its not even clear how it should in some cases