Hi,
I'm 6'1" and am very tall in my upper torso. I never have a problem finding a seat that covers my shoulders. I don't know the exact depth, however the lounger and 12 jet corner therapy seat are both very deep. You will find, like many, that you're not wanting to be so low in the water for a very long time anyway. However, when I tested the Bengal vs. the Prodigy, the Bengal had much more depth to it even though they're both 33" tubs. Its just the way they designed the TR with more sculpted seats.
I might be able to get out a measure mine, but unless you're extremely tall, this shouldn't be a problem for you.
Mark