Mike - this might be the correct thread. As far as I know, Bistro has no dedicated thread, so it's either this thread or the firmware thread: https://budgetlightforum.com/t/-/32545.
The bottom line would be asking the author - ToyKeeper, and her firmware thread would be the better of the two since she created the other one.
I just looked the code over and it seems you are right - 1/2 second delay in the main loop, then the "overheat_count", incremented by 1, has to be greater than 15 to do an adjustment, and when it does an adjustment, "overheat_count" is reset to zero.
So it doesn't adjust for 8 secs, then only will adjust every 8 secs or so thereafter.
Also be aware it adjusts one "level" per drop-down adjustment, and there are 64 levels defined for the full range of brightness/output.
All I can offer for my explanation is that Bistro was written for single LED DD lights in mind, for the BLF SS/Cu X6 or Cu X5 class running at 4-5A. Also I can say others have seen this problem and tweaked the algorithm. You can bump up the decrement factor or bump up the frequency of checks, and/or add intelligence to do it smarter. Dr Jones got his own PID algorithm implemented for temp monitoring, but has not released it to the public. I heard Atmel has a sample PID in source code as well, but will probably not fit in to a 25's 2K.
Yes - you are right about the 80 seconds. Here's the top 11 levels for FET PWM values:
129,137,146,155,164,174,184,194,205,216,255
I agree, a triple in a thin tube light is a crazy design when it's fully max'ed out. I would never put one in the hands of someone who is in-experienced with these sort of things. Bistro is just the firmware, and not designed for this intended use, accept for the fact it's given out open and freely in source code, so the designer of a flashlight can mod it as they like.
You also might want to consider a turbo timeout - set the timeout to 30 secs, and it drops one full mode, which could be down to 35-40%, depending on you mode definitions, but of course temp monitoring has advantages for more circumstances.