I think the buzz has less to do with tenon size and more to do with methods. Most come from a dry joint. Dry because of the adhesive used. Epoxy will soak into both the forearm piece AND into the handle piece, leaving very little, if any, to hold the two pieces together. When a buzz ring is used, the glue doesn't soak into the phenolics as it would into, let's say, maple. Also, longer tenons have more surface area for glue so run less of a risk to aquire the buzz.
Brush expoxy on all surfaces of both pieces and let them sits for a couple of minute. Watch what happens. Apply more glue and then connect them together.
Use too thick or too much epoxy and you run a risk of hydraulic pressure splitting the bore side of the connection.
There is no such thing as a one-size-fits-all with adhesives.