Not sure what the deal is now that they changed the start time of the elites, but here was my experience for 2017.
I received an unsolicited email from the BAA months after I registered letting me know that I was among the top 10 seed times (2:30:52) for my age group (45-49) and, as such, would have to wear front and back bibs which would be provided at the race.
Based on that experience, my guess is that if you are in that top 10 in your age group, you will be notified and provided with whatever opportunity is appropriate to compete for a money finish.
The one quirky thing is that some of the masters runners did end up in the elite field - ahead of Corral 1 of Wave 1 - based on times on downhill courses. I think some masters guy ran 2:22 or 2:24 at St. George or another race in Utah and was up with the elite field as a result. So maybe that will be an issue.
For what it is worth, I ran my 2:30 at Chicago on a decent weather day, was seeded maybe 15th or 18th in the masters field and fifth in my age group with that time, and ended up 3rd in my age group and 13th masters with a 2:34:40 on a very hot day. I think the top 3 masters were Abdi, Meb and Clint Wells. Needless to say, top 5 was definitely a tough ticket.