The wider tyres are fitted to the rear of the ones outside the US too - most "modding" owners go the opposite - wider tyres both ends for obvious "looks" and grip reasons.
I did once watch an older Smart understeer and ping into a kerb in Edinburgh on a cobbled road during a typical summer day (i.e. lashing with rain
) and wondered about the narrow front tyres. Apparently Austin 7 (1926-39) owners use Smart front tyres as the originals are hard to get hold of these days.
Handling - My Aygo has 155/65 x 14 Continental EcoContacts which seem OK for grip. When I first got the car in July I ran at the factory tyre pressures (34-36) until I got used to how the car handled. The one thing I did notice was that the front tyres felt like they were rolling off the sides when cornering really hard - kind of like tyres felt when I was driving in the mid-80s on 135s
So I upped the pressures to 45 and now it feels pretty secure.
My car is the opposite of yours - front engine, front wheel drive.
I don't rotate my tyres as I prefer to replace them in pairs - the fronts go first, so I replace those and put the older rears onto the front and the new ones on the back - understeer is preferred.
Good luck with the change.