my plants have larger or smaller flowers based on many things - temperature is a big one. if it is high summer and the plants are getting tons of light/heat they grow so fast that they bloom out smaller flowers. once the heat dies off spring/fall i get the larger flowers. this is especially apparent in the garden varieties. of course other things can affect the bloom size too - fertilizer/water you name it. of course there is the winter/summer color changes too....
Thank you very much