Tight lash setting solid flat tappet cam

I'm currently running a Comp Cam XS274S SFT at .012/.014 lash RHS iron heads and hughes Al rockers. I set lash cold and have .001 change cold to hot. Comp cams specs the lash setting at .016/.018
When I installed the RHS heads I knew a future cam change was going to be necessary to get the most performance, but I'm thinking of closing the lash a little more to increase duration.
Anyone have real world experience doing this?
What's the tightest lash anyone has run successfully?