What protocols are used for Thermage to prevent fat loss on the face?

Hello, It is my understanding that thermage tightens collagen but can also be used for liposis. I want the former but not the latter and have heard that devices used incorrectly can cause facial fat loss. Are there certain protocols I should ask for, ie a maximum temperature or is it the number of passes used or the power? do wattage or frequency affect whether collagen is targeted or both fat and collagen? Thanks for your help .