IAX - Follow-me - hopefully not a huge mistage

I’m trying to complete a very basic set up including and IVR that will allow the caller to pick an extension, and then the person they are trying to locate will attempt to be found using follow-me. Though i was encourage ny the person that initally set up asterisk to create a new extension for each phone number n(so in my case 3 extension (i.e., work cell and home), and then move them into a ring group. As I’m currently using ringcentral (i’m guessing asterisk based), i already had extensions assisnged and cards issued to 40 to 75 consultants both in the US and europe, so I followed the advice of when of the posts, and i created extension 101-150 and 201-225 and used follow me to track down the individual.

From what i can tell, this seems to work, but occasionally is seems as if it skipped a number that was to be the #2 of 3 locations. I do have a domestic all you can dial DID and a back-up with Lesnet, 2 pay as you go international carriers, and 2 incoming only lines from China and the UK. Should setting my extensions and follow-me in IAX in theory work? It does seem to be willing to dial numbers that are not just IAX internal extension (such as cell phones). Is this realistic? If so, do I really need to create sip accounts for the consultants that will be on the road? It seems to me that i can’t tell the difference on my end betweem a SIP call and an IAX call.
Thanks in advance for any help you can provide.