SamMcClintick ... you have the right idea, that it is different according to the person!
Sometimes one needs to raise the table/machine height to make it work.
A small rise under the legs of the table can do the job.
Likewise, you may need to raise/lower your chair accordingly.
Generally, the ergonomics are ....
Feet flat on floor
Knees bent at 90°
Hips 90°
Arms flat on sewing machine table top with elbows bent 90°
Shoulders resting easily, not hunched up, or dropping down.
Of course, these are generalities.