Bias Psvane we845 for Line Magnetic

I've the same topic here. 
Did you get any answers so far?

Actually I let the WE845 run for 2 months with the same bias as the stock 845 tubes. 
I needed to readjust the bias a few times.
These days I found out that the V2 WE845 can't even reach the middle line at the bias meter, although I've adjusteted the bias to max.

I don't know what to do exactly, need some help here.

thanks.