FWIW, Taka and Reynosa Senseis explained it as
"Thank you for what you are about to show me," and
"Thank you for what you have shown me" (respectively.)
Yes, you're asking a favor, asking the other person to potentially have his/her body abused for the sake of your learning.
Perhaps as important is the simple spirit beneath it all, a spirit that you'll learn through practice in the dojo, if it's there to be gained. That is appreciation for both the senior and equal/junior members of the dojo, for that they're making the opportunity to learn and grow available to you.