Everyday Systems

i usually eat less at breakfast than at lunch or dinner. Thus, there is always empty space in my plate.

Does the three plates rule require plates of uniform size?

Will it impair my habit creating if each meal has a different size plate?

I usually have bowl for breakfast, a smaller plate for lunch and a 10" plate for dinner that I don't fill to the rim. So yes, plate size can vary.

I agree that plate size can vary. And if you are not adversely affected by having space on your plate, no worries. There is no obligation to cover the plate.