OK, guys,,,I'll give it another shot.
You want to start your crosses in a way that the majority of your pulls on the crosses are going under the last main on the outside of the string bed.
This has nothing to do with the last cross string, rather, with most of the crosses.
For example, on a Youtek Prestige Pro, which has a 16 x 19 pattern, and I'm stringing a normal one piece pattern, my first cross would go under the first main I encounter. This ensures that crosses 2-18 are being pulled under the last main string on the outside of the string bed.
The theory is, that by going under the outer main on the pulls, there is less friction, and as a result, a tighter string bed.
Hope that helps.
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