I was never very confident with the nomograph presoak methods that were advocated with many of the kits back in the 70's and 80's. What temperature did the developer climb to and what was the effective temperature over the course of the developer cycle? Measuring the temperature of the small amount of developer at the end of the developer cycle, especially if using the minimum in an 8x10" drum, was very difficult.
I'm now using a method that I believe is about as accurate as you can get when using a "drift-by" technique. I use a Simmard (raised rib) 16x20" drum. I use 2 litres of presoak water for 1 minute. It is poured in at 103.5deg. F and exits at 97.5deg. F. The developer (1 litre) is poured in at 97.5F. At the end of the dev. cycle the developer is collected for replenishment. The developer exits the drum at 92.5F - hence a 95deg. F average temperature which is the recommended temperature for the brand I use. I should point out that I'm using a developer designed for tabletop equipment that wasn't totally convertible from the EP2 to RA-4 process. (My developer time is 105 seconds versus the normal 45 seconds for today's RA-4.