Wind seldom blows at 45 degrees to my destination (or 40 degs, or whatever best angle is possible with a given boat-sail-rudder-leeboard envelope at ideal conditions).
But you do sail up wind, don't you? If you sail upwind, and tack, so as to arrive at any destination that is within the 90 degrees of "in the irons" or stall (45 degrees each side of wind direction at 0). You will want to sail as close hauled as your configuration allows. If your destinations NEVER exists in this dead zone, ignore this because you will always be able to get where you're going on anything
> close reach. -and must have the luck of the Irish,
-May the wind always be at your back.
If your destination lies within 45 degrees of 0, -wind direction, -you are going to want to tack as close hauled as your configuration will allow with out stalling. Let's say your destination exists at 30 degrees of 0, starboard side, 5 miles away. This just means your
close hauled port tack legs will be longer than your
close hauled starboard legs (the tack names are counter intuitive), but they will be as close to 45 degrees as your configuration will allow.
Looks like I will end up with a few feet of line covered by continuous stretch of graduated marks

.
Close haul, close reach, beam reach, broad reach and running, those are the places to mark on your sheet.

Close hauled is the most important because you can't sail closer than close hauled, though your sail may continue to appear full. You will stall, making either no progress, or pitifully slow progress, as the wind pushes you back about just as much as you are going forward.
Because point of sail changes every time when I change my course. Or - when waves push me off course. Or - when I round the point or approach the shore (wind pattern is always different around points or close to shoreline). I wrote about this, though.
This is sort of the point I'm driving at, but if I am genuinely
sailing up wind and my destination continues to exist in the "dead area" my tack legs are going to be
close hauled, or I will
never arrive at my destination.
When rounding points, or approaching shore, wind direction may shift meaning a new point of sail is indicated for that condition. Your destination will not have changed, unless your objective was to get around the point, then of course you have a new heading.
Also, close-haul angle opens wider when waves are getting higher.
This is called leeway. It's the same principal as with a glider. A glider can be pointed to the horizon, but it's going to eventually come to the ground before it gets to the horizon. Wind blowing from your weather side is always going to push you slightly to your lee, -which is the whole purpose behind leeboards, to minimize this. That is why if your genuine destination is at close reach, you may want to sail at close haul so you actually hit your destination without needing tack legs. The stronger the wind, the greater the leeway.
(For this latter reason the closest angle on one side of the tack is not the same as on the other side - because direction of waves doesn't coincide precisely with direction of wind).
No the direction of the waves isn't always precisely with the wind direction it's also affected by currents and tides. This just means that due to leeway, compensation is needed by means of longer opposite tack legs. The point of sail hasn't changed, just the symmetry of the tack legs.
This is why I wrote that didn't find telltales useful on upwind course - they are always straight streaming. They are more useful on low-wind downwind course, of course.
OK, fair enough. This is why I would recommend at least marking your close haul position on your sheet. It will completely eliminate the guess work. Cleat your close haul and then trim your rudder until the tell tails stream straight from your luff. If you have accurately determined your close haul when you marked it before, you will now be at close haul again, -the point of maximum efficient upwind progress.
On downwind sailing, anything broader than a beam reach, the tell tails tend to bend down wind of the luff. They have only marginal value here in determining point of sail.
The rest of what you are saying I concur with. Just as my boat tends to sail differently than a
real boat, I imagine a FC may sail differently than a Klepper, -also depending on mast configurations, etc. I'm still tuning my boat to improve performance, with some really great results. I've found kayaks are a great deal more sensitive to tuning than bigger boats. I keep talking about getting a furler for the jib, and I may yet someday.
As far as motor sailing: I've also found this necessary. The problem is that in motor sailing, apparent wind actually begins to effect actual wind. Your sail can be trimmed for pure sailing, but if you paddle, it's going to effect the apparent wind, which will effect the sail trim. So this is a case where the apparent wind you are creating will cause your more efficient point of sail to be boader than 45 degrees of actual wind. To find this new close haul, if you have your sheet marked for close haul, you would simply trim your rudder until the tell tails stream straight from the luff.