But I like to look at things in an extreme example. That helps to better understand my madness...
So you have a direct fired heat source under your mash kettle blasting away at your return wort in which you pump directly back to the top of your mash via some plumbing. Let's say as an extreme example your return plumbing back to the top of the kettle is 50' long, causing you in theory massive heat loss, causing you to have to heat your lower heat source wort to dang near boiling (or whatever) degrees above your desired mash temp just to maintain your exit temp for the top of the mash. You have to super heat the wort under the mash, (including the lower portion of the mash) well beyond your set point to accomplish this.
The reason I designed it this way is first, the friggin tee is VERY cool and used in other applications such as cooling on the kettle! And the fact that there is no utter way my lower mash can overheat my set point of the system while I worry about the top of the mash. The mash will play catch-up until the whole mash is at exactly where I want it to be...
Your system may have different reasoning, but in a direct fired mash, I think it is more important to pay attention to the lower mash. The upper part of the mash will get there just fine by itself... Cus once I reach my set point of say 152, and nothing in my system got above 152, and 152 degree wort is constantly being recirculated through the whole mash from top to bottom, and the ASCO is dead silent because I set it to 152 because the whole system reached it, then I am simply at 152.
