What NTRP rating combinations works best in 18 & over Mixed? More Interesting Tennis League Stats

It is time for 18 & over Mixed teams to form in my area for the 2016 season.  This is an early start league for us so we use our early start ratings that just came out, but a common question is what the makeup of a team should be.

USTA rules allow for there to be a 1.0 rating level gap between players which means at 7.0 a 3.0 and 4.0 can play together, at 8.0 a 3.5 and 4.5 can, and you get the idea.  But the question always is if these non-balanced pairs do better or worse than a balanced, e.g. 3.5/3.5 or 4.0/4.0, do?

I've looked at this before for 7.0 and 8.0, but I thought it was a good time to take a look again and get a bit more specific and detailed.  So here goes.

In each case below, the first level is the male and second is the female.  And I've looked at the various different combinations to have a complete picture.

For 7.0, here is how it breaks out for the 18 & over Mixed leagues over the past few years:

• 4.0/3.0 vs 3.5/3.5 - The 4.0/3.0 wins 60% of the time
• 3.0/4.0 vs 3.5/3.5 - The 3.0/4.0 wins 52% of the time
• 4.0/3.0 vs 3.0/4.0 - The 4.0/3.0 wins 57% of the time

Here is the same for the 8.0:

• 4.5/3.5 vs 4.0/4.0 - The 4.5/3.5 wins 61% of the time
• 3.5/4.5 vs 4.0/4.0 - The 3.5/4.5 wins 51% of the time
• 4.5/3.5 vs 3.5/4.5 - The 4.5/3.5 wins 60% of the time

And the same for 9.0:

• 5.0/4.0 vs 4.5/4.5 - The 5.0/4.0 wins 57% of the time
• 4.0/5.0 vs 4.5/4.5 - The 4.0/5.0 wins 58% of the time
• 5.0/4.0 vs 4.0/5.0 - The 5.0/4.0 wins 51% of the time

As before, it appears the unbalanced pairs will generally do better than balanced, and the unbalanced with the higher rated male is going to be stronger.  But it does change some by level with 9.0 being the most different.

Now, of course it is going to depend on the actual ratings of the players involved.  For example, at 8.0, two strong 4.0s are likely going to do better than a weak 4.5 and weak 3.5.  But the stats above are from looking at tens of thousands of matches the last few years so tell us what happens on average.

What do you think?  Do you have an explanation for why unbalanced seems to rule?