GL-P, clarify a few things for me, will you? I don't understand:
You: You see, composites don't like being shaped around hard curves. They tend to break easier.
Me: 1st sentence: why? 2nd sentence: Based onnnn...?
You: Big fin fillets are used to act like cross supports at joins.
Me: Fin fillets serve an aerodynamic purpose. Big fillets don't seem to do this; they just seem to increase surface area. Also, if they're "too big", you wind up with two more anomalies:
-the joint becomes stronger than the individual attached parts.
-the flightward-facing fillet area needs to be tapered and contoured in relation to the height of the fillet. Hence, more "necessary" surface area (for the proper aerodynamic component) and "unnecessary" weight (weight is not our friend).
You: A rocket going mach needs all the help it can get!
Me: A rocket needs little help with "going mach" other than a zero AOA (assuming proper construction and pursuant building technique(s)). Period.
After about M 0.8 and with increasing velocity, EVERY structural component - airframe, nose cone, fins, airframe joints, fillets - starts to become air-dammed or dirty air generators. Hence, one needs to minimize surface area.