Rhubarb - problems with 'new' crown

A friend of my wife's has a lot of rhubarb (which she doesn't even like!) and she gave my wife a crown last winter. I planted it in a nice, sunny spot (the soil is a bit 'clay-like' but I added some good, free draining soil to the hole before planting the crown). I made sure that the tip of the crown is a bit above soil level (I understand that they rot quite readily).

It's growing, as in leaf buds appear and grow into small leaves. However, this is where the problems begin (note: I've never grown rhubarb before!):

a) Sometimes a small leaf that emerged a few weeks before will turn yellow and drop off.

b) The remaining healthy green leaves (I think there are around 6 at the moment) never seem to grow particularly large - they must be about 4 inches across and seem to remain that way. The stems don't seem to grow much either, I guess most are maybe half an inch in diameter and about 6 inches long, if that. All are horizontal, not growing vertically (I always thought that rhubarb leaves grew more up than along).

Is perhaps all of the above because it's not only early in season but because this is a relatively newly planted crown?

There's no sign of slug or snail damage (although my ground does attract a lot of them).