Question IRS Tax Question if paid outside of Chapter 13 plan

[azphoenix]

Hoping someone can give me a little more clarification on how this would play out. I'm a little over 3 years into paying the 5 year (60 month) plan Part of the payment plan is IRS debt from 2018,2020 and 2021. The 2018 tax debt was suppose to be paid by my ex-husband in the divorce decree( it's almost $9,000). However, he has been making installment payments from previous years and has not gotten to the 2018 taxes as of yet (it's almost been 5 years since the divorce). The 2018 IRS tax debt is included in my payment plan because the bk/ or IRS does not care about the divorce decree. After speaking to my ex-husband today he said he may possibly be taking out a loan and paying off the 2018 taxes. I spoke to my attorney also today, however I feel I never get a straight answer or it's always wrong once things happen. My attorney said we could possibly lower the payment amount in the plan once the 2018 taxes are paid. I would have to pay him $750.00 for a modification plan and redo my income and monthly expenses. Does this sound right, that the courts would allow my payment to be lower if the 2018 taxes are paid in full outside the plan? The 2018 taxes had been filed jointly. From my understanding the court and trustee would keep the same amount and then just pay more of my unsecured debt that was not going to be paid. I feel like somehow I would be out $750.00 for modification of plan and also my bk plan could of been less if my ex-husband would of paid them off before I filed my BK. It was 2 years after the divorce when i filled Chapter 13. Sorry, very confused on how this works. Thank you for any insight you may all have.