Radishes

I have been harvesting my radishes.  Selectively.  I'm trying to harvest the largest radishes first.  I've noticed that I can't really tell, from the foliage, what size of radish is underneath it.  Some of the radishes have great huge swathes of leaves, but produce a very ordinary size radish.  Others, with much smaller numbers and sizes of leaves, produce very large radishes.  I find this very interesting.  I don't really know what it means.