Increase contrast and midtone separation in Fuji Acros?

Hey guys,
I'm shooting Fuji Acros in 4x5 and developing in PMK. I want to do a series of 4x5 cyanotypes with the negatives. What can I do to increase contrast and especially increase midtone separation? Will shooting at ISO 50 help or hinder me here?

Thanks,
Chris

Try an 18pct solution of EDTA salt.