There dosent seem to be a particular rule of thumb so best imo not to try and apply logic
On the other hand just as an example the Renault E Tec top model Iconic went down from over £5000 to less than a £1000 now
And there again the Nissan Qashqai e-POWER jumpted up its original AP by £800 overnight
AP has/can flutuate for many reasons that are not always known to us
We can counter by doing our homework and keeping an eye on available dealer offers and asking local dealer to match
Extend lease to take advantage of any late quarter offers
I am sure others will add to this and give their take on the matter