Louis -
Like my last post, these comments are a general response to the topic for other readers as well, so for the highly experienced anglers, please forgive the lecturing tone.:) Especially as ground is covered that you are already very familiar with, or may have different ideas about. Matt?:)
As I continue to ponder, I guess what I don't know is when a big trout closes on a fly when it sips. I know to wait a while when I see a big head come up and eat, then head down, but with a little sip rise made by a big fish how long before the mouth closes? It's hard to envision the fish turning down, since he's not showing much of himself anyway. Any thoughts on this?
The same previously mentioned principles apply, though I admit the toughest fish to hook are the big boys sipping tiny flies requiring a downstream presentation. They're typically slow rises with little down turn. An angled set helps, but the line to the fish is still pretty direct and there's a good chance that you'll pull that tiny fly between his big teeth or scrape one of them for a bump, or maybe even have him on for a second or two. There are some things you can't do much about and a missed, felt, or farmed fish is not necessarily the angler's fault in this situation. The odds are much better on an oblique or upstream presentation, but sometimes you can't get away with that. Sometimes a little beetle pattern on a short shank offset hook helps and I always have a few on hand for such an emergency.:)
Then there are the quick sippers... They can be truly maddening!:) What these tricksters are doing is hanging about six inches below the surface and tipping up with minimal effort to suck down something tiny every few seconds. The just show their noses and you'll find big beezers doing this in really good (meaning tough) lies with abundant minutiae on the water (tricos, midges, thick spinner falls). It's tough enough to get them (or yourself) to find the fly, let alone hook them. Again, sometimes the beetle pattern mentioned above or a tiny Wulff will do the business,
but on these guys you have to be pretty quick. The good news is they will often give you multiple chances as they're pretty confident. I've often seen bumped fish start to rise again in short order. BTW, you bump a fish in this situation, change flies and hope he'll stay up.:)
The bottom line is to recognize the riseforms and visualize what can't be seen so you can react accordingly. Spotting fish from an elevated position where you can clearly see the goings on is the best way to learn them. Take note of how the water surface is disturbed as well as what the fish is doing, as often that is your only clue. While there are broad categories, the truth is there are as many different riseforms as there are ways birds fly or where balls lay on a golf course. Not having enough opportunity to get out is a handicap, just like it is for a golf swing or shooting eye, but having the right principles ingrained is still a big advantage. Just like in those other sports execution comes after recognition. Blind execution doesn't increase the odds of success.