Iv got a tiny 7inx4in plate on my cruiser as it’s an American import and the holder is made for a small US size plate, iv owned it for 3 years since it was imported and never been pulled.
Iv got a full size plate that I put on for MOT day and it looks absolutely ridiculous fitted.

On a side note the last MOT tester said it’s not a fail to have a mini plate fitted as long as it’s easily readable but it is illegal to ride it on the road so you could literally ride out of the garage after it passing and get a ticket for an illegal plate