If I understand the basics of thermodynamical aspect of engines, any turbine engine has by default, at SL, too much air supply from the N1/NG stage which starts to dissipate at a certain altitude, where normally N1/Ng will be the power limiting factor (or maybe TOT in hot environments, but not TQ).
Correct me if I'm wrong but R44 doesn't have any super/turbo charger to get the air supply up? The air supply to the engine than drops as soon as you go higher than SL.