Unrolling and used RAMs

Channel definition:

channel float channel_float_sink;
channel float channel_float_vector;

It seems strange to me the direct correlation between the Unrolling Factor and the increase in the number of used RAMs blocks. As long as I increase U, the block usage increases. Which doesn't seem only due to pipelining.

My first guess was that, since M20Ks have only two ports, the more you unroll, the more blocks you need to support concurrent operations.