Fixed awning sensible?

The calculation is quite simple, there are online tools for that. Very simplified, if, for example, the awning ends at 2 meters height and the sun shines at a 45-degree angle, then the "sun shadow" is also 2 meters. For all more precise calculations with time of day etc., there are online tools.

Yeah. When is it like that? Autumn/Spring? If I sit on the south terrace in autumn/spring, then it is to catch the last/first rays of sun. You don’t want anything over your head then. By the way, you talked about a 4m deep awning – yes, and then at this time of year you probably only have 2m of absolute shade, 3m warm legs, and beyond that also sun on your face. 2m "sun shadow" does not mean that you would be blinded over the full 2m if you were in this 2m zone.

The valance can bring down a few more centimeters, but only if the valance is oriented towards the sun. If the awning is on the south side and the valance goes towards the south side and the evening sun comes from SW, WSW or W, then the valance does nothing.

The orientation of the awning is fixed, sun positions are not. That is inherent in the system and you won’t solve it. Therefore, like any other sunshade, it is not perfection. You would need very large sunshade systems to always reliably have your lounger in the shade. Or the sunshade is mobile or the lounger is.

Manufacturers also offer vertical side panels mounted to the wall that can be pulled out. But mostly more as privacy screens, the sun will still sneak over them from above.

Sunglasses help against the rest.

As said, when that is the case is stated above. This also applies in the absolute height of summer. The sun being at a 45-degree angle is rather rare. Usually, it stands lower.

Sunglasses offer little protection against sunburn.

I am currently wondering whether a market umbrella or a significantly larger sunshade with a low west side makes more sense.

Where do you live, or where do you want to build, so that you are craving shade? This probably concerns only a few hours a year and most likely you are either working or doing something in the house at that time anyway. These calculations are absolutely negligible: plant a tree in a nice spot, under whose canopy you can then sit.

Haven't you already answered the question yourself [emoji6] As I understand it, you want to protect yourself from sun exposure due to variable sun positions. You have proven with your calculation that a permanently installed sunshade inherently reaches its limits.

To me, it sounds like you need a more flexible solution for protection with variable sun positions. Whether a fixed sun sail can do that, I doubt. It sounds to me like your wishes cannot be met at all times.

That basically leaves only the cantilever umbrella, which offers the necessary flexibility as long as its base is not concreted in.

My personal choice would definitely not be an awning, they are too old-fashioned for me and I don’t like them visually. I find valances terrible. Then I might as well move indoors. An airy asymmetrical sun sail or a cantilever umbrella would be my solution, with a slight preference for the airy sail, although I don’t have your level of flexibility requirements.

A freely positionable cantilever umbrella is the most flexible, but also the most flimsy. grym, if every sunbeam is too much for you, just don’t plan your terrace facing south. It even saves money, you can take a cheaper plot. I mean it seriously, the south-facing terrace is planned wrong for your wish.

Awnings are affordable, after that come stationary solutions costing multiples. Take a look at the current models from Markilux and the like, it has nothing to do with grandma’s awning anymore.

I have to admit, some of the markilux awnings are quite pleasing. However, personally, I somehow prefer sun sails. But I don't understand why high-quality cantilever umbrellas should be considered lousy. They just cost a fortune if you want something decent. Depending on the situation, they can fit the house less well or even better, don't you think?

I like the hint about planning the terrace. Maybe the OP should address the causes rather than trying to fight the symptoms. With a south-facing terrace, you can definitely expect some sun... [emoji6]