How is the distribution of Argo floats managed over the Earth's oceans?
I think, there are two factors which prevent the forming of clusters of floats:


The floats' lifespan. Batteries supposedly last for four years, then the floats become debris which sink to the bottom of the ocean (yeah, not that great from an environmentalist point of view). So the lifespan of the battery prevents the floats from clustering.
The introdcution of new floats. Derelic floats are replaced by new ones to keep the network working. Naturally, these new floats are placed somewhere in the ocean, where they don't end up immediately in a gyre but will most likely provide the most possible diversity of data.