What should cold lash setting be?

Good afternoon all! Got a question about valve lash settings. After running my Arrow for almost two seasons now I finally was able to get the cam card from the previous owner/engine builder. It's a Bullet cam, solid roller, 276/285 duration @ .050, gross lift .685/.682, and cam card says hot lash should be .026/.026. I'm running CNC ported W5 heads so what would the suggested cold lash setting be? I'm thinking .019? But I'm no metallurgist and not sure what the expansion rate of the metals involved would be. I have Harland Sharpe 1.5 aluminum rockers.
Also, as an interesting side note, when I bought the car the previous owner had the valves set at .018 intake and .020 exhaust which obviously isn't what the specs call for. Why do you think he deviated from the manufacturer specs?
Thank you!
cold =.006 tighter than hot ...