Hi Stud, welcome to community. I am not too familiar with this mixsmsn or what you are trying to do. But I, or other folks here might be able to help if you provide a reproducible example (often called reprex for short).
A reprex makes it much easier for others to understand your issue and figure out how to help. A lack of a reprex just makes it much less likely others will reply.
Your question is very close to a reprex, but we'd need your library/package loads, and you'd need to setup Diameter1 for us.
Having said all that, (and again, not really knowing much in this domain), are the three modes you're confused about listed mu 21.634 1.539 12.499? Looking at the histomgram, those appear to be the three local maxima.
Note super zoomed in at 21, a little jump up.
