Your coil will be attached to the output of your pump, where flow restriction is OK. In fact, flow restriction will be NECESSARY. If you open your pump fully during the mash circulation, it will likely compact the grain bed and cause you problems. (Been there, done that.)
I wish I had realized this sooner, because I actually heavily modified my 3/8" IC to use as a HEX. I wanted as little flow restriction as I could get, so I cut the coil in half and put T's on it. 1/2" pipe goes to a T, two 3/8" coils flow in parallel, then back to another T and out through another 1/2" pipe.
All of that work was TOTALLY unnecessary. To get a good flow rate during my mash, I have to almost completely close the ball valve on the output of my pump to avoid the compacted grain bed, so I could have just left the 3/8" coil as one single piece instead of cutting and soldering a bunch of stuff together.
Oh... and my 3/8 coil is 25' long.... or I guess I should say it WAS 25' long. It's now two parallel coils, each 12.5' long.
Only brewed one real batch so far with it, but I have played with it a lot and it seems to be working fine.
Ground Fault Brewing Co.