I heard that to benefit from BE you have to play small mouthpieces. Is this true?

No. You can do the BE exercises on any mpc. It is possible that in the process you want to change mpc's; your embouchure will change!.Typically, this tends to be a somewhat smaller mpc (diameter, cup), but that is not necessary. Some people are perfectly happy with bigger mpc's and still benefit from BE. In the end the choice for a mpc depends on what feels good for you, what sound you want to make or what sound you need for a particular job.