My take on the CG requirement . . .

NavAid bouys suffer from bird splat and damage problems, so for a small
device the enclosed feature of the Mobri makes sense. The big'uns have
retroreflection built right in to the structure, or an actual racon.

My take on the issue is unless you have a large (or sluglike) boat that
doesn't mind the windage of an effective (read expensive) permanent
mount reflector, a Davis EchoMaster raised high on a burgee halyard in
the catch rain position is reasonable. It's light weight, unaffected
by heel and moves around enough to mask null return problems. Fix a
few strands of yarn on a corner so it doesn't spin like a banshee in
high winds and snarl its halyard.