Um...
For Double Axes (with Rajas and Brutal, although w/o it doesn't make any difference as far as I noticed):
< 16% TP return - at least one miss
16% - full Rampage w/o DA
17% - full Rampage w/ one DA
18% - full Rampage w/ double DA
Below 16% is a bit complicated - if you get 11% TP return dmg isn't as much gimped as you will get 12%-14% TP return. I would say that 11% TP return is more dmg than 15%, but less than 16%.
For Axe/Sword (with Rajas and Brutal):
Just take 1% tp from any of above.
XI Wiki

