If the orig aspect ratio (width / height) is below or equal to 1.5, switch to EAspect.LetterBox. If not, leave it at EAspect.Crop (like in Vocaluxe before).
Unfortunately the acinerella library, used by Vocaluxe, don't support reading of the DAR value of the video file. So the SAR value has to be correct in the video file, to see this automatic in action.