Originally Posted by Streak
Conclusion - I am a very unconventional swimmer and none of this makes any sense to me.
But what you describe matches my experience perfectly. Decrease SR and SPL drops. Times also get slower. You feel more relaxed and less effortful.
Increase SPL (i.e. to 18-19 from 16-17) and speed increases. (This is true only up to a point, and only if you are doing some things correctly, as it's possible to increase SPL without increasing speed).
So, none of what you posted surprises me at all, or seems unconventional.