If the RHN had more or better subs, they'd have played hell with Italian logistics. Each slowdown causes a ripple effect further down the line. The Greeks had some aircraft rated as torpedo capable, use them in that role to attack shipping in Albanian ports or close to the coast. While nighttime flight ops are extremely dangerous, courage was the one resource the Greeks had in abundance. In OTL the RHN attempted a raid or two with DD against Italian convoys, without meeting any. If they succeed with one or both, the RM will be under pressure to utilize heavier and or more numerous surface escorts, which detracts from the forces needed to counter the RN, etc etc. More ripple effects.