I have never heard of anyone using a fuel cooler. In most cases peoples cars are using all of the fuel that they are sending to the engine so its usually not sending enough back to the tank to need a cooler. If your fuel is heating up enough to affect the car you may need to look into one big pump or something else along those lines. as far as the flex fuel sensor goes, it goes on the return side after the regulator I believe. not 100% on that.
OP, What fuel are you using E-85 ? how many pumps if multiples? and why do you think you need a cooler?
The flex fuel sensor is best if installed directly after the regulator,( more isolated from the elements) occasionally you may run into a problem with the sensor flow through being to small this will/may cause the regulator pressure to go up in the higher boost pressures if your 1:1 like most. what regulator are you using? Return line size?
Personally I run a -6 return from my Weldon regulator but the -6 is teflon so it has a larger interior volume then standard rubber-6 and as of yet I've had no issue with a fuel backup into the regulator(^pressure) at over 40 psi of boost and 1100+ hp.
95 RHD SUPRA fully built bottom end Ferrea head 1mm over fully ported 74mm Bullseye,Tilton Quad,TRD lsd,Getrag 1319 hp at 45 psi on E-85 Megasquirt MS3Pro BUILT at Big Daddy Performance Tuned by Jordan T Turbo Jew