The country size choice for currency production in 20th Centruy paper money seems to have deen determined by ease of production rather than other factors.
In European countries, the size of note was slightly larger – in width or height, and sometimes both, as the denominations inclreased in value.
These countries produced one denomination on each sheet of paper.
In the United States, starting in the colonial era and continuing thru the early large size note prodction era of the 1880s, the format many US printers used were notes of the same size, so that one sheet of four notes (as they were often printed) could mix and match denominations for the same issuer. So a note sheet may include a format of 1-1-3-5, or 1-1-5-10, or 1-5-5-10, or other formats.
The uncut sheets of Colonial and Continental Currency which are extant also show that several denominations were included on the same sheet of paper.
Thus, for ease of production, namely cutting, that the choice is made for same size currency.
(Granted since the larger format presses have been used, I know of no modern production facility which still mixes currency denominations on one sheet of paper).
So the size issue, is one of historical production convience.
Thus the court rule, as reviewed in the NY Times article, now puts the response to the Bureau of Engraving and Printing, who, I must say is really on a learing curve, starting with the redesign of the currency since the 1990s with the “big head portraits”, and now with color.
Sadly, I think it is still the vending machine industry in the United States which will keep us from getting different size currency.