SD-WAN VPN to multiple locations with multiple ISPs

I'm working on learning the capabilities of the FortiNet SD-WAN features.  Using this guide https://community.fortinet.com/t5/FortiGate/Technical-Tip-Configure-IPsec-VPN-with-SD-WAN/ta-p/209840 I've been able to connect SiteA and SiteB, each with multiple ISPs.  The SD-WAN features are working correctly and I'm quite happy with the setup.  Now I'm bringing SiteC into the picture.  SiteC's setup should be no different than SiteB really.  The question is at SiteA.  When I'm setting up the SD-WAN zone for connections between SiteA and SiteC, do I put the connections under the same zone that's used to connect SiteA and SiteB?  Or would I want to create a completely different Zone? 

Background, big picture, end game, if it makes any difference, is Hub & Spoke but then enabling the Route Reflection (I believe it's called) so that SiteB and SiteC can talk directly together without all their traffic going through SiteA.