Reading with interest as the seed potatoes that I buy here in Brittany are significantly smaller than those I used to plant in the UK. I find that I sometimes have double the quantity of seed for the same weight. All of them are smaller than a hen's egg.
Years ago I was planting them like I did on my allotment - even though they were smaller, and my neighbour told me I was planting much too deeply. Ten years on he still teases me that if I plant them like that they'll come up in Australia instead of France(!)
I do a compromise now. The real tiddlers go on the compost heap (and probably produce potatoes there!) But anything bigger than a walnut gets planted. But I don't plant quite so deeply anymore.
In my experience large tubers produce larger tubers. I alternate the sizes putting a large one next to a small one. My DH once asked why one plant produced lots but the next was rather poor. He had not realised what I was doing.