SSDI & Workers comp 80% rule

I know that a person collecting both SSDI & WC benefits are limited to a total of 80% of prior monthy earnings. If a person has been awarded SSDI benefits and then sometime into the future is awarded WC lump sum (back benefits + interest) how is that calculated as far as SSDI goes. Do they count the total amount towards the 80% or do they deduct the attys fee and then apply (or break down the balance into the # of months SSDI was recieved) and see if the person is over the 80%? What if there were benefits also paid to children by SSA. This is confusing.