I went a little different direction this winter with part of my plan testing
20 min power at 80% of max HR
4 min max power
1 min max power

The formula given by the author (Cody Waite) calculates my FTP from those values very close to what I've done in the 95% of 20 min after the 5 min blowout test, the 2X20(5) test and what I've done for a 40K TT.

He also calculates ratio of aerobic power to VO2max power and suggest efforts according to it.

I'm not entirely drinking his kool-aid but it's a different direction that I decided to try.

It sounds like you're talking about running. It's hard to get an estimate of power, like in cycling. Setting aside the whole issue of the power meter insoles for runners, what you might actually care about here is speed at V02max. That's measured on the treadmill while measuring your VO2max. Measuring the speed will tell you about your running efficiency and other factors than just max oxygen consumption in L/min or ml/kg/min.

Or if you don't have easy access to a lab, just do a 1-mile test on the track once in a while. That'll give you a pretty good estimate of speed @ VO2max.

Max VO2 speed (running) or power (bike) can be measured with some protocol.

MLSS speed (running) or power (bike) can be measured also.

But what do you call aerobic power / speed ?

4h maximum performance ?
10h maximum performance ?
Iso energy (fat/CH) power ?
MaxFat power ?
Power / speed at 1,5 mol/L lactate ? (or any other value between 0,8 to 2,5, or 4, or...)

If you train for LD tri or ultra trail, VLaMax (the lower the better) or fat oxydation (the higher the better) are good references to define your training, but these are not power/speed.

Lactate level is an interesting reference, but not easy to use every day.

You can choose HR reference, such as 65% or your MaxHR (base endurance) and then track the corresponding running speed in a given course.

In the Science of Winning, Jan Olbrecht defines "Aerobic Power" as follows:

"Aerobic power is the percentage of aerobic capacity that can be used during an athletic
event. The higher the percentage, the better the aerobic power. Various metabolic factors
prevent an athlete from using 100% of his aerobic capacity during the event. The lactate threshold or
maximum lactate steady state is a good measure for the aerobic power. Aerobic power is directly
affected by the anaerobic capacity. The higher the anaerobic capacity is, the more it becomes difficult
to achieve a high aerobic power."

So, based on Olbrecht's definition, it seems there is a strong correlation between MLSS and
aerobic power. So, maybe all you need to track is your speed/power at MLSS and use that
as your aerobic power estimate.

OK, understand.

Yes, of course there is a correlation with MLSS or Max VO2 speed/power.

But when Albrecht say : "Aerobic power is the percentage of aerobic capacity that can be used during an athletic event."

this % of course depend of race duration.

For exemple :
if you plan to do a 70.3 in 5h (as an exemple), you are probably going to use an aerobic power around 83% of your MLSS / FTP (not exactly same thing, but...ok)

If you plan to do a full in 10h, probably going to be around 73% of your MLSS.

For the last exemple, of course it is better to be able to do 74 than 71%.

If your objective is multi-hour, then the key is fat burning (low VLaMax). This will drive all your training, with a lot of work in base endurance and some sweet spot.
If your objective is 20mn race, then it is a different story.

This was part of my original question. How do you track "aerobic power" in
a manner that is not event/duration dependent?

Aerobic power is inherently duration dependent.

But the shape of the power curve can be anticipated based on some parameters. However, the parameters are not the same depending on the duration zone :-)

Sebastian Weber seems to consider the curve can be anticipated largely from VO2max and VLaMax (if I understand well).

From some of the sample INSCYD test reports available, aerobic power is not one of the
things that it's reported there.

The best lab test is a race.