I think that they discuss how to specify a tension when you have strung different mains & crosses tensions somewhere on the Sergetti site, although that doesn't address your specific question...perhaps email them. A guy called Serge is very helpful. I have asked several detailed questions and always received an equally detailed response.I got as far as going to the website and inputting my Racquet (yes the Prince ported ones are there) and strings, nat gut / poly hybrid.
Then I got to the tension, interesting - there's only one tension.
I typically like 4-5lbs more tension on the gut mains than the poly crosses.
I've even experimented with as big a difference as 10lbs and in low winter temps liked the feel of this.
Question will I lose the feel I get from a mains / gut differential?
I note that the claims do not include extra spin.
I'll swear that a gut/poly tension differential gives me more spin and better life span of the gut mains (fray less quickly, retain snapback longer), and longer before the poly goes dead..
What should I make of the one tension for mains and crosses in his method?
I did want to mention that FYI, in my experience, the tension feels a bit higher than normal using Sergetti i.e. 45lb Sergetti is feeling about as stiff as 47/48lb traditional.
That could be my limited stringing experience, but I do recall someone else making a similar comment or seeing something on the Sergetti website in FAQ