Nathaniel,
The Somers flute I owned had an embouchure where the blown side chimney wall was cut to a significantly different angle than most flutes I’ve owned/played, which is to say that the angle slopes away from from the player (is more undercut), than the majority of modern simple system flutes you find.
Gary used an angle, at least on my flute, that was very similar to most, but not all, Sam Murray flutes I’ve run across. IME a more steeply undercut blown side embouchure hole requires a different lower lip placement on the headjoint relative to the embouchure hole, and/or adjusted blown airstream angles for the registers , otherwise you can have intonation and possibly playability issues.
Keep in mind that where your lower lip is placed relative to the near side of the embouchure hole can affect overall sharpness/flatness due to having a certain amount of your lip overhanging the edge and impeding airflow out of the embouchure hole: Remember the embouchure is also a tonehole and your lower lip is shading it somewhat, unless you happen to play with your lower lip well back from the edge. I think many players going for a reedy tone, myself included tend to play with the lower lip in a position where it is interacting with the embouchure hole aerodynamics (shading a bit) and then we unconsciously compensate for the induced flatness by “playing sharper” - rolling the headjoint, lipping, adjusting size/speed of the airstream etc., to get to pitch.
Also related to all of this is are your “normal” blowing angles - how much you blown down vs. across for each register affects your pitch on a given flute, and these angles are based largely on the aforementioned lower lip placement, as well as the amount of lip pucker or lack thereof, and the rotational axis of the flute. Now change the flute embouchure undercut without changing your blowing angles (and or lip position relative to the embouchure hole), and you can maybe start to visualize how and where problems with pitch and playability can occur.
While some people may seem to adjust unconsciously to the relatively few flutes with outlier embouchure angle cuts, others may have trouble. Additionally, some players, typically the better ones I suspect, are well aware that they are needing to adjust to these flutes, but they aren’t bothered by it. Finally, there are people who are aware of the issue when they run into it and are able to adjust, but find it really annoying to have to do so. I fall into the latter category and as such sold my Murray and Somers. Both were very good flutes, but I had to play them significantly differently than 98% of all the other good flutes I’ve run across over the years, so I just found it…..not fun to play on those flutes.
To be clear: I don’t find the good Murray flutes (and not all of them are good) difficult to play, nor did I find the Somers flute hard to play, I just found it distracting to play those because my lip position and blowing angles are significantly different on every other flute I own and play regularly, so for me, why bother? But that’s me, and the Somers can be a great flute for many people, it just has to be played differently than many other flutes out there.
Finally, there is certainly validity to the idea that a certain maker could be a sharp player, but a fair number of Somers flutes were made and I don’t recall hearing a bunch of stories about them being flat, that’s something Gary would have sorted quite quickly and easily if it had been a thing. I suppose there could be a scenario where you have a very early model where he hadn’t sorted that yet. Seems low on the list of likelihoods though as I suspect Gary would probably have recalled the flute and made it right.
OK, hope something in all of that is helpful Nathaniel. I’d start by experimenting with lower lip position and blowing angles while using a tuner and see how that affects bringing up the pitch. Failing all of that….. well I’m reminded of a T-shirt I was given as part of a multiday auto rally racing school I went to (shout out to Team O’Neil) the back of the shirt says “blah, blah, blah, ACCELERATE!” Maybe we need a Flute player shirt that reads “blah, blah, blah, BLOW HARDER!” Hmmm, maybe not. Still, when flat and in doubt, blow harder! Just joking. Mostly. 