SURPAC reporting different digblock grades between the two different methods

Hello,

I am running into a problem when I try and get the digblock tonnes & grade out of our grade control model. When I got Block Model > report and then constrain by string and segment it works but is a bit time consuming. The other method is block model > BM grade control > code polygon from block model which is giving the same results in the tonnes but grades approximately double as to the other method. Is there any reason that this might be happening? I must be doing something wrong but really can't see what.