The influence of temperature
I agree with Per, at least for sunk line fishing. The technique of tightening/striking must surely depend on the speed at which the fish moves, which is affected by water temperature. Given that this is also the governing factor for choosing floating or sinking lines, it is reasonable to say that the technique should differ depending whether you are fishing floating or sunk. I can only speak for atlantic salmon here, so things may be different for steelhead.
Fishing a sunk line (eg on the Tweed in autumn) the conventional technique is to keep the rod tip low and wait until you feel the weight of the fish come properly onto the line. In slow water a fish can nip a fly several times during its swing, and attempting to strike would ensure that it immediately lost interest. When (if) it takes properly, a fish may pull several feet of line off a lightly set reel, and you just lift gently into it and then clamp down on line or reel to set the hook. At other times the fish just arrives and a steady lift is all that is needed. I would add that I almost never fish a hook larger than # 6 - above this size I turn to a tube or waddington - so there is no huge thickness of iron to drive into the fish's mouth. This must affect the degree of force needed to set the hook.
Fishing with a floater I, like Adrian, tend to have my rod butt tucked under my arm, and the act of moving it forward before placing it into the stomach 'feeds' the fish a bit of line, which is taken up again as I raise the rod. Doing this at a sensible speed without rushing seems to get the timing about right (it's hard to be precise). I also tend to have a small loop (maybe 18") of line which I release. By contrast, a great fishermen I know fishes with a high rod point (about 45 degrees). On seeing or feeling a fish take he drops the rod tip to give a few feet of line, and then raises it again to engage the fish. Both techniques seem to have about the same success rate, and from the point of view of what happens at the 'business end', I guess they produce similar results.
One thing is certain: fishing conventionally for salmon, you should never strike. Probably more fish are lost that way than any other, and it is the hardest thing for a trout fisher to learn when graduating to salmon. There are 'minor tactics' where striking may be desirable (article in this month's 'Trout and Salmon' magazine for example about just such a tactic), but they are the exception rather than the rule.
As to which way to move the rod, just look at the geometry a bit. With 90' of line out, moving a 15' rod from pointing directly down the line to being at 90 degrees to it (which wouldn't be the case in practice anyway) only changes the angle of line from rod tip to fly by about 9 degrees. As Per points out, the effect in minimal, whether this angle change is in the vertical or horizontal plane. I prefer to get as much line out of the water as possible, to get on direct terms with the fish, so raise my rod vertically.