I just buy them, blp does have nice, easy to read stuff for sure.

I have never been able to actually get totally myopic about size variances, unless it's like a miss print where something is crazy off.

I'm usually just either going bigger, or smaller, till it's as close as I can get it. So perfect sizing doesn't really bug me. Besides, after tuning on the dyno where at least things are consistent. The in car results always seem to want more fuel, or changes in the whole cure because of scoops, or heat ect.
Then factor in the time to change things, get the car cool, and try again, the air has changed again.

I suppose a PS, or comp tuner would sweat all that, and have a sure fix for everything, but getting to the edge of a tune where .001 difference in a bleed would matter with carbs seems unattainable to me . For me it's make the curve safe enough not to do too much detonating on shifts, and clean on the top end.