Ed, you'll have to convert the final ratings into percentages though. Ie, how much more likely is the 10 going to win than the 16.66'??

Rank might be judging skill, last round finished judging form and h2h might judge matchup. Problem with h2h is you have to know why one player has beaten the other. Was it experience vs inexperience? Surface? Style of play? Injury? Home crowd etc.

It might be possible to come up with tennis rankings using rank and recent form, and then make adjustments for h2h, matchup, surface etc. Think it's better just trying to create power ratings than using a simple formula. Try it anyway (on paper or something), see how it goes.