An Emerging Master of Smart Practice Planning
There's an elegant "mathematical logic" emerging from your practice planning and execution. You must gain an exciting sense of circuits being constantly honed and improved.
For instance, your Stroke Length circuit improved "automatically" as you halve the distance. I'm not overlooking the aspect of this being a planned outcome on your part, but pointing up that most people have a kind of vague expectation they'll go faster when they shorten a repeat -- because swimming for less time means they can go harder. But you're doing something very specific and unquestionably salutary - increasing efficiency!
Also your analysis of sensing you're hitting a wall of sorts at 14 SPL. I agree entirely. Your analysis that you have two ways around that wall - extend repeat distance or increase tempo - is likewise right on. In fact, I'd say at your height, any effort to get to 13SPL will bring diminishing returns. Far better to swim longer at a given combo of SPL and tempo, or gradually reduce the tempo at which you can hold 14SPL - and every count above it in your current range.
I imagine you're starting to gain this sense I've had from time to time of "inevitable improvement." There are few things cooler in swimming.
Head Coach & Chief Executive Optimist
May your laps be as happy as mine.
My TI Story