Portion sizes, well, that also, even in France depends on taking a la carte or a menu. A la carte portions should always be bigger. Son was in the trade and that is what he says should apply, always.
I only ever see menus at lunch time in our bit of the UK. And portions are just right. A la carte main dishes seem to be rather big, but shouldn't they be, to reflect the price difference.
ps, not talking about nouvelle ripoff cuisine....