Dealing with Armiger Helverins

I’ve been playing a friend and his Helverins are wrecking me because so much of my stuff flys (wraiths, c’tans, DDA, HLD’s) that had good strength/AP. He can camp them in the back with 12” moves and long distance firing I can’t stay out of sight lines with my reduced movement speeds comparatively. I tried using a warrior blob to screen but that’s mostly inefficient. They are high wounds and decent invul saves keep me from using immortals or other volume fire to plink him down. His 150 point guys are easily out trading me. Anyone have some tips for me?