I think the reason your "catch" ratio has gone up is because the fly/lure you are using stays in the strike zone longer plus it is being moved around by any current and looks more natural to the fish. When using a spin/casting rod, you cast the hardware out there and immediately crank it back and the only fish you will be catching are the aggressive fish who will be striking as a reflex action. This will only hold true with fishing artificial baits and not live baits since live bait will usually be fished under a bobber or on the bottom which will allow it to be in the zone longer than a crankbait/spinner would be. A fly rod allows the bait/fly to flow naturally in the water and look more like something to "eat".

My opinions only....