I believe the large portion of offers below the clearly-in are due to guarantees for SEAS applicants. Without applying for SEAS, I don't think you will be made an offer if you are below the clearly-in. I am also not sure able how likely it is for you to be made an offer in subsequent rounds. The demand for the course is extremely high and I am not aware of anyone who has gotten in below the clearly-in without SEAS (although I do not claim to have spoken to everyone in my cohort).
I'm sure that while most second-round offers are for those who received SEAS consideration, I do know of several people in my cohort who received second-round offers for Monash biomed without SEAS. Granted, most of these people were quite close to the clearly-in.
As I understand it, SEAS will not give you a guaranteed entry into a course unless explicitly stated. What does matter, however, is the calculated weighting of a SEAS application on the 'raw' ATAR. Presumably in the situation I've described, the ATARs of those who received second-round offers were (likely) still higher than some others even with SEAS.
Hence, OP, definitely preference biomed first of that's the course you want to get into. If you don't do that, and preference instead a course you're essentially guaranteed entry to, only THEN do you not give yourself a chance.