I don't think his problem is a drop in DP, it would have to be a severe drop to impact his efficiency since his recipe is mostly 2-row (or did you mean to post this to Martin's thread on DP?).
Just shooting in the dark, but could this be a percentage of starch/sugar available difference? Less well modified? Perhaps the new grain has more moisture content throwing everything off? Like I said, total shots in the dark.
I wanted him to be aware of this potential.
There are so many variable involved in measuring efficiency that it becomes quite an effort to accurately measure with a high degree of confidence. If the weights and volumes are accuratey measured, the water pH is measured, the temperature is accurately measured and the gravity is measured correctly...etc...
All of these measures are required and must be performed fairly accurately to obtain a good measure of efficiency. If one of these variables gets away from you, there will be error in the measurement.
This brings me back to DP...