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I was holding back from commenting because I have heard folk expressing contrary opinions on this.
However, in my own experience, which is limited to just two occasions of checking the clearances and where shim adjustment was required on only one of those occasions, my findings were that ......adjusting the openers affects the closers and therefore they have to be done "in sympathy" with each other.
This was done about 10k miles ago and all seems to have been well since then.
As I said, I have heard folk claiming that the adjustments for the closers and the openers are independent of each other, but that was not my experience.
If you haven't already checked out Chris Kelly's video on two valve shim adjustment (Ducatitech) I can recommend his method of checking the closer clearance via the opener shim .. its much simpler and in my opinion is therefore more accurate in the final analysis, despite being an indirect measurement.
Finally, many folk advocate "sanding" the shims on fine emery to achieve exactly the shim thickness required.
Personally, I would not do that as these shims will be hardened and then ground to accurate levels of squareness and offhand "sanding" could well disrupt that geometric accuracy.
Std shims should give you all the accuracy you need to get the clearances within the recommended tolerances.
The above is just my own opinions but, without wishing to pull rank, I do speak as one who has engineering training and experience.
Hope that helps.
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