Try not! Do or do not! There is no try!
I responded to you on Aikido-L.
But some additional thoughts...
My sensei often reminds us to continue our attack. You are attempting to attack nage from the point your start your attack until your balance is taken and your are thrown. When you say that your tanking I'm assuming that you strike and then don't budge? Yep, that can be frustrating to nage. But the response isn't the opposite to fall sooner, it's to find sensitivity to nage's movement.
This means you need to relax and maintain your connection to their center, and respond when you feel your center changed. To me tanking happens when a person stiffens up. Let go and go with the flow some if they take your center then they took it but if they didn't don't just go down to make them feel good. Sensei often says that you should be loose and pliable.