Thanks for your replies guys.
KBAR I think you are right the vehicle is 16cm in length as compared to say the holdall which is only 2.5cm, so what you say makes sense. As I say its not really a problem as I can go below size 1, I just need to type the size in the field.
BEZO I checked to see if I had enabled "Keep Visual Size", but no I hadn't.
I did wonder what was happening for a while, when you get past 60 years old it does sometimes feel like you are losing it, only for a minute or two though. 🤦♂️