Well, my concern is why the small flowers to start with? I know several people here on the forum grow almost all there plants in pots and buckets and they seem to have normal sized flowers. What type of "soil" do you have in your buckets and how large are your buckets?
I just solved a mystery NOID I had in the garden, it was a transplant of a division of 'Whooperee'. The clump is a nice size with nice foliage, but the blooms are noticeably smaller than the original clump of 'Whooperee'. Glad they were blooming at the same time. What jogged my memory was that that same day I also transplanted a division of 'Lady Neva' right next to the 'Whooperee' division and 'Lady Neva' bloomed today. I don't actually remember the blooms on transplants ever being smaller.
I have some proliferations I planted last year in small (2 qt. maybe) pots, I hope at least one of them blooms this year so I can see what size blooms can be expected.