Bear with me through a bit of a story until I can ask my question...

I grow many Gesneriads and have quite a few Saintpaulia. But, I grow mostly in isolation from other growers. A few months ago, a fellow AV grower sent me two or three plants. When I received them, I was amazed at the huge leaves and thick petioles. They had very few leaves, really, only 10-12, but they were very large.

After a few months on my rack, the new growth is coming in smaller and I'm going to guess much more rapidly based on how many leaves they are adding a month vs what the grower told me regarding how fast her plants are growing. I've almost doubled them in terms of leaves, yet they are only a fraction larger as I've removed the older very large leaves and the newer smaller ones are taking their place.

So, my question is this....what causes a plant put its energy into producing many small leaves vs adding fewer leaves and putting more energy into making them large leaves?