This answer is likely out there but I am wondering if anyone knows off hand what the optimum starting point for all three of these could be. I know the measure the bore trick. But I am curious. I thought I placed a cork well on a Rudall style and was really out of tune over the scales and octaves. It is incredibly humid where I am right now, and even with air conditioning everything seems to have swollen so I am waiting the weather out for adjusting. I have a nicholson Olwell that is in the right place and wonder if it would be the same for the rudall headjoint if the bore size is the same. And I do have a Terry McGee pratten which I I might have accidentally moved or not. HaHa.
I think you just need to place the cork in whatever position it needs to be in for the octaves to be in tune. I put it this way rather than stating a specific distance, or set of distances, because I think it depends a bit on how you blow. And it depends on how the maker tuned the octaves when voicing tone holes etc, and what assumptions they made about how to blow.
For me, I always need the cork further away from the embouchure than the 19 mm head bore and traditional rules of thumb would suggest. And this is regardless of whether I’m playing a Rudall or a Pratten or other models. For me its often more like 21-22 mm. But the important caveat here is that I don’t worry too much about the third octave.
How much you care about the third octave is an important factor. If you are only playing ITM and want a strong low end, and typically won’t go into the third octave at all, then you might want to place the cork further back from the embouchure than if you were playing music that spent a lot of time in the third octave.
And then there is the more subtle issue of how you like your flute to sound in terms of the harmonic mix etc. I can notice some subtle differences in tone and voicing depending on how the cork is placed.
In my opinion, stopper placement is a bit more of a multi-factor trade-off than we are usually led to believe, initially.
I would have to measure it to be sure, but I think the last time I adjusted the stopper on my Peter Noy Nicholson style flute, it was pulled back slightly from the standard bore measurement position to balance the first two octaves. Again going by memory, I think I’ve done that with my two previous flutes – a Windward (Pratten-ish?) and an Aebi Rudall style. Just a tiny bit to the left of the embouchure (for a right-handed flute). But that’s me and how I blow a flute, not all that relevant to anyone else.
I believe it’s important to figure this kind of thing out by playing tunes into an RTTA (real time tuning analysis) software app that will show the variation of pitch for each note during the recording of the full tune, so you can see exactly how the first and second octaves compare. And then adjust the stopper accordingly.
This is far better than looking at a digital tuner where you might “chase the needle” in a way that’s different from how you actually play the tunes. I use the RTTATuner app on my iPhone, there are others available.
Thank you. I agree. I am stuck playing up to the third octave B due to shared tunes in local sessions. Though I was recently reminded that B responds better if it tilt my chin up a bit. 
My recent experience of thinking I was playing in tune was dashed in a new to me session with 6 whistles, pipes, banjo, a flute and a guitar. The piper who is a pro with an excellent ear focused on my flute as being quite sharp and had my pull out the headjoint a good half an inch for what he perceived as an in tune A. That whacked out the whole scale and set me to questioning if what I thought was a good setting on that headjoint was totally and absolutely wrong. I’m playing the unkeyed Nicholson for a while until the weather permits a good sit down. I did comparisons with all my flutes which I think play in tune with a pencil line on a dowel rod and found a wide variety of placement.