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The "average" American stands about 6' tall - 72". Figure your eyeballs are mounted about 4" below the top of your head. So, the "average" person has a maximum standing eyeball height of 68".

On the other side, one can quickly figure a normal and comfortable seated position of body height minus the distance from knees to hips. (Think about it, or just just look at how you sit now - your thighs are horizontal and contribute nothing to height when seated). For most people this is around 40".

Thus we have a normal comfort range of 40" to 68". Any shorter and you need to "scrunch" while you sit. And on the other end, you need a 4" tall step. For a 68" radius arc corresponding elevation angles are roughly 34 degrees and 71 degrees. Attached is pdf which illustrates this. Of course YMMV by body size and how efficiently the scope is designed and built.

Maybe in Texas. Only 15% of American men are as tall as 72", half are below 69", and very few women are 72" (Census round-off error makes this number 0.0%), the half point for them is 64".

So, subtract 3" to 8" to bring the comfort figures in line with the real average values. It reduces the max height for standing 6.5 degrees and 14.5 degrees respectively (to 64.5 and 56.4 degrees).

But if you live north of 49 degrees (the U.S. Canada border in the west) the ecliptic never gets above 64.5 degrees anyway.