This thumbnail plane is technically a "Roman" profile and not really "Grecian". That is to say that the arch of the curved profile is not elliptical. However because of the way the arch is laid out on the plane, changing the spring angle can give you an elliptical appearance to the profile. Holding the plane at about 30˚ will give you a more true Roman profile while holding the plane at about 25˚ will result in more of a Grecian or elliptical appearance. It may not seem obvious but if you held the plane and used it you would see the results and why you can achieve this with a simple change.
Here is the video below. I think the only thing I might add to this video that I didn't mention is that you may want to back up the cross grain cuts if you experence exaggerated blow out on the lower portion of the profile. If it is large blow out then it may not get planed away when making the long grain cuts. If that's the case, just place a block of wood equal in thickness to support the wood behind the cut and you will be fine.