Determining new child support amount

I have been divorced for over 9 years and pay child support to my ex wife. Two years ago she obtained a new job making a significant amount more than her previous job. I have been trying to renegotiate with her based on my current monthly salary less bonuses and funds I have to pull from 401k each month in order to pay her what is owed. She is refusing to share her current salary and wants 3 years worth of my W2’s and my 1099 ,forms while she provides nothing. My understanding is that child support is based on your monthly salary only, am I correct. If she continues to refuse to provide her current monthly salary I have a ball park idea as to how much she makes can I begin to pay that amount? I pay for the medical insurance for our two children and we spilt all other expenses. Thank you for your guidance.