Estimation from models, right? I have somewhat high (for my age) short power that falls off steeply after ~15 seconds, and run into the “modeling problem” from time to time. Xert always appears to over-estimate my HIE / W’ (see above: What is your W' bal(/anaerobic capacity) in Kj? Did you work to change it? - #20 by WindWarrior) while WKO usually appears to under-estimate FRC / W’.
Ok, they (HIE, W’, FRC) aren’t the same, but bear with me. One reason is that it is challenging to do all-out short efforts. Mostly mental, I find it really hard to keep pushing beyond 15-sec. Probably part mental, part physical. Whatever.
Right or wrong I’ve accepted what some coaches say - that W’ changes slowly if at all. Here are some estimates from WKO:
Models can be noisy, right? Especially models that aren’t always fed good data 
What isn’t shown are the time spans where I know the model has good data.
So with that coaching assumption, I wave my hands like a good engineer and declare “my FRC is 18kJ” which seems reasonable if you agree it changes slowly if at all.
And then I hardcode WindWarrior’s “eFRC” along with modeled dFRC and use that on graphs for workouts that reduce anaerobic capacity, like last night:
and of course I normally leave dFRC hidden and only show WindWarrior eFRC on that graph.
Yes I know the model is a rough estimate and there isn’t a good algorithm for replenishment of W’/FRC. And a side note: about 2 weeks ago modeled FRC was 16.7kJ, and since then a really hard, maximal type ~15-sec sprint fell out of the 90-day window used to estimate FRC. So FRC dropped as expected.