A full and very informative blog post here, although the English is a little stilted in places: Capping
I would just make a couple of points. First, it is always possible that businesses could be split into distinct legal entities to avoid the rules. Second, the last paragraph of the post points out that many wealthy estates benefit from large CAP subsidies.
However, this brings us back to the question of what the CAP is for. If its main objective is to help poor or marginal farmers, it is an inefficient means of doing so. (Actually, there are probably at least two objectives here, one an income distribution objective and one a rural landscapes/depopulation objective).
If one, however, one thinks that the CAP should be helping European farms and food processors to be globally competitive, larger farms are, in general, more efficient (and often more environmentally conscious and aware of animal welfare needs).