Also about the knee bend. How much of it is knee bend vs back bend? I tried to do a deeper knee bend but I see most videos kinda lean back A LOT as well with the bend. Maybe I'm doing it wrong but when I tried it my back was telling me that it doesn't feel too good...
OH, one more thing. I'm not tall (5'7") so are there any tricks or tips to have a more effective serve? (jump for serve? little spin?, wicked spin?)