Nickel Plating on .012 thick steel per QQ-N-290 Class 1 Grade C

We are making an EMF shield for a customer. The material is .012 cold rolled steel. The specification is Nickel Plating per FED-QQN-290 (replaced by AMSQQN290) Class 1 Grade C.

Because the material is so thin it is often flexed or bent during the plating process.

When we had the parts plated, initially the coating was too thin, about .0005" but otherwise seems to work okay. When the full 001" thickness was put on the plating cracked and separated from the steel when we tried to straighten them. The thinner coatings were dull and the thicker coating was almost mirror bright.

The specification refers to SB, SD and M. Would it make sense to specify the Class C SD to get a coating that is not bright but would be more likely not to separate during the straightening operation after plating? Also is spec if any SD allowed because the specification seems to indicate that SD is not allowed for Class C even though its allowed for all other classes.

Neither my customer or I am knowledgable about plating and my plater is reluctant to make a recommendation.