why not start at or just before the lands
Then I would wonder why you did this.
After all, there is no reason for a seating number pulled from nowhere to be right.
My reasoning for testing and testing first;
In my experience seating testing is vital to best accuracy. Assumptions here are not prudent.
Also in my experience seating testing has a far bigger affect to results than powder testing. That is, seating testing(actual testing) is the coarse adjustment, and powder is the fine adjustment.
And with anything calibrated, you adjust coarse first, then fine.
Tweaking seating for group shaping is not seating testing(it's tweaking).
OCW helps you locate a desirable powder node. It doesn't even consider seating, and that's fine because seating has nothing to do with powder. But my thinking is that it will be easier to see best powder at good seating rather than bad to begin. Your ladder should look better too.
Keep in mind that many from 'the other school' have been accepting or outright declaring for years that VLDs needed to be jammed to shoot(as a rule).
Yet most of us actually testing did not find that to be true.
Berger's seating testing procedure has enlightened more.