Since the requirement is for 360 degree visability I believe masthead is all that is legally acceptable since the mast will block a portion of any lower light.
As a practical matter...we used a Davis
Anchor light above the bimini to insure that we could be seen by power boats and others who were not looking up 65 feet. Never had any law enforcement issues with this approach...but we DO have a masthead light as well...just didn't use it.