Temp controller issue, honeywell

[biggubba]

I built a rims system similar to the brewmagic setup, I am having issues with johnson controls temp controller that i used for rims hex (heat exchanger). I have it built out of 1 1/4 stainless and is inline on output (return side) of pump. When recirculating mash, it is consistently 6 degrees cool than brewmometer on mash tun. Any advice would be appreciated, temp probe is in a drywell which is on outlet of hex.