While hooking the fish is the ultimate goal, it is only part of the equation. As to hooking, all the discussion about angles and such are probably not really important when the fish clamps down on the hook thus possibly rolling it sideways. Timing when setting alone is, in my opinion, more important and we really cannot even control this a lot unless seeing the fish up close as it bites. More important to me is how the fly swims. I like straight eye for helping flies swim straight in the water, Up/down eye hooks tend to lever the fly in up/down angles. Other factors do play, weight in the fly, current, retrieve, etc. The construction of the fly to "lay level" as most food sources do naturally in the water, is what I strive for. Fishing in current and deep in the water can require a heavily weighted fly that will be fished under tension, making it swim level. A special note: on smaller flies the knot tied to the front can result in appearance of the fly being longer. For this reason I was shown use an up or down eye hook run the line through the eye, tie a knot that secures to the head of the fly blending in the size of the fly. This also is used to create "pull" from center of hook rather than the offset end of the eye of the hook. Not really complicated, just need to think a bit.