When calculating SD in my rifle(s) I run 3 20 shot strings at DIFFERING days and conditions in match like order on various practice days at different ranges.
This is the ONLY way I feel comfortable using a particular load for 1000mtr comp.
All of my comp loads run ES of 5-8fps, but a little more really makes little difference vertically, wind plays more of a zephyr at most ranges here.
You can look at SD as how uniform your load is in generating consistent start pressure, without this, your load is erratic and will have high ES regardless of how tight it may group @100-200yrds.
It must be understood that a high SD/ES number does not mean a load is inaccurate, it only means that beyond 500-600yrds the vertical dispersion is too large for true precision shooting.
I have a 25-06 load that prints 3/8MOA @ 300mtr and less that has an ES of 80fps. Not ideal beyond about 400mtr, but awesome @ 100mtr.
This demonstrates that barrel time/harmonics have a direct influence on accuracy, this load, even with it's large ES is coinciding bullet exit at 2 points that match in the oscillation and, often when a load produces 2 distinct 'groups' in a string from barrel harmonics being different, this is the cause.
Cheers.