I am no newbie to gardening but I noticed something this year.
I had a BUNCH of starter tomatoes that were ready to put in bigger pots. I started all of them in 6-cell starter packs you would find at the nursery's. They were all the same size for the most part, really all the same size except for a very small number that were not doing well but that was only a VERY FEW and only one variety.
I up-potted them all at the same time. I ran out of 4 inch pots and had to put some in 5+ pots. Only about 1/4 of them were put in the bigger pots. All were placed in the same soil mix. Same lighting, same everything.
So why are the ones in the bigger pots at least 25% bigger and beefier than the ones in the smaller pots. The variety range here is all over so that in my mind shouldn't even be taken into consideration. Like I said they were all the same before up-potting. This was noticed very soon, and with time they seem to be getting even bigger.