There is no change in tension. A string of a particular diameter, strung between two fixed points, and tuned to a particular note will be unaffected by the length of the string beyond the nut or bridge.

It is true.
I find it much easier to tune a guitar with six on a side tuners that point up, than to tune one on a reverse headstock.
When I taught guitar there were times it was expedient for me to tune the students' guitars--although they all learned to tune--and the ones with reverse headstocks were pains in the butt.

Along the same lines--and in reference to what you're used to--Most of my guitars have the tuners three a side--and that is actually what I am most used to--and I find it much easier to tune and change strings on the upside than the downside--and I am used to both.

In fact as the unwound strings are usually more likely to break, I have changed more high E strings than any other string. And that's on a tuner pointing down. The string most likely to go out of tune is the G. And that's on a tuner pointing down. So what am I most used to? Yet what do I find more awkward--despite being more used to it?

As far as my 12 string goes--those six tuners pointing down are the worst.

It's more natural and intuitive to tune and change strings with the tuners pointing up.

That said, I wouldn't pass on a guitar that I otherwise loved, just because of a reversed headstock--and hey I love my 12 string--though it can be a pain in the butt to change strings and tune. But all other things being equal--a regular headstock would be my preference.

String length does affect tension to a point. That's why Les Pauls are recognized and feeling different and Taylor sells short-scale neck lengths that are touted to feel different - because of the scale length.

But since it really doesn't matter how long the string is BEHIND the nut, I wouldn't think you'd notice any difference on the same neck, whether it's normal or reversed.

I have never heard a gibson player say he prefers tuning the bass stings more than the treble due to tuners pointing down...Maybe its because you guys tune via the 5th fret method, and are using your picking hand to make tuning adjustments. I have not used that method in years, so t is easier for me on a reverse, since I use my left/fretting hand to tune. Many pro's have to tune on stage durng a song and that is why the reverse headstock works better. You rarely see a pro using the 5th fret tuning method

I just don't see how moving your hand from playing position to over the top of the neck is easier than keeping your hand in playing position and just reaching for the tuners. Especially if you have to make a quick adjustment mid song

The physics of a string don't change due to the length of string on the other side of the nut... tension of a given brand of string of a given gauge is the same when the string is brought to pitch regardless of how much length reminds behind the nut.

I therefore share Vulkan's opinion.... the only thing a reverse headstock does is make you personally feel more like your favorite lefty rock star and make you wish you hadn't done it when you have to tune the guitar.