Yes, that’s true for Seikos in my opinion. Ideally, the rate would be the same at 230 degrees as it is at 280, but it always changes to a greater or lesser extent for any watch. In my experience Seikos and Miyotas etc show a bigger variation, even though the positional variation can usually be adjusted to the COSC range of 10 secs at high amplitude there isn’t much that can be done to improve isochronism. Generally, the ETA offerings are significantly better and watches such as the Rolex 3135 and Omega 8500 are better still........but you’re paying a lot of money for these! I can adjust and regulate a Miyota or Seiko to keep very good time on my wrist based on keeping the movement in a high state of wind , but as soon as that watch goes to an owner who is far more sedate the performance is likely to differ, its a lot easier regulating the better movements such as the Omega 1120 or the TAG or Breitling versions if the ETA movements provided they’re in good condition. They’re also very efficient self- winders so they’re more likely to remain in a high state of wind despite the relatively modest power reserve of 40 hrs.
Not sure if the answers on this thread answer tge original question but hopefully they've proved thought- provoking. Mechanical watches are fascinating items, the technology should've died in the 70s with the advent of affordable quartz movements which are infinitely better at the job, but it didn’t. I’m struggling to think of another technology that has survived in this way despite being superseded by something better.