Do I have to use the same group size for dual batts?

Hey guys been doing lots of research here and on other sights about dual battery systems. I am getting conflicting info on same or different size batteries on a dual system. I have a 2010 CM Platinum so I have a 27f as my main and it looks like I can only fit a 35 on the other side where the windshield reservoir is now. I like the 27f size and was wondering do I have to keep the same group size on both? I will have only a bed mounted winch and inverter hooked to the aux battery and everything else to the main. I will be using an isolator hooked to the system so I could really use some help with your guys expertise. I’m in a quandary, so waiting on your knowledge. Thank you