Lync 2013 - Number of FE servers in paired pools

Hi,

We have an Ent. Edition Lync 2013 pool with 4 FE servers, we would like to implement a second pool at a different location for disater recovery.

Does the DR pool which will be paired with production one need to have exactly the same number of FE servers or can it have less (i.e. 3) ?

Thanks for your help,

Luca