Recalculate progression defaults to Optimal Decay

I was playing around with decay settings wanting to see the impact on my fitness signatures over time.
When I recalculate progression it however defaults to “Optimal Decay” no matter what I set as Decay Method before recalculating.

Is this a feature, bug or something else that I do not know about?

I use Chrome on Win10 but have tested on Edge with the same result.

I’ve found something similar however it’s that the profile every so often reverts to optimal regardless. I set small decay as I’m endurance based and seeing this decided to check it, it had reverted to optimal again even without me clicking recalculate.

I thought changing the decay setting only affects future declines or lapses in training unless you use the method below to recalculate from ‘original activity’ after which it reverts back to Optimal.
Did you save as Original before clicking Recalculate?

Maybe the setting also reverts back to Optimal whenever Xert is updated and there is a limit to the number of days you can divert from Optimal.

You can’t use No Decay when performing a progression recalculation, since No Decay uses the data from that progression to make estimations on fitness from your current training load. When you recalculate progression, you’re wiping out that historical relationship, so there’s nothing for the No Decay algorithm to work from, which is why it defaults back to Optimal.

After recalculating, you can then switch to No Decay and flag/unflag an older activity to recalculate the progression from that activity using No Decay. It’s best to only use No Decay if you have sufficient (and accurate) training loads and fitness signatures.

I have tried all the decay methods and for all of them it reverts to Optimal Decay and the terminal signature and the TP+breakthroughs for the last year (at least) are exactly the same.

Thus I suspect that it is only possible to recalc progression using the Optimal Decay algorithm?