The altitude capture phase (Airbus and Boeing) is a result of computation of ROC (ROD) and vertical distance between current altitude and FCU/MCP target altitude, hence the wide range of ALT* observed. BUT the really important thing is that once this phase is engaged the autopilot and/or FDs will now follow a geometric flight path or trajectory as calculated at the moment of capture. i.e. it will follow that path regardless of all else and that include a loss of energy for any reason (e.g.windshear or engine failure) The aeroplane will sacrifice speed if necessary to maintain that path. Some aeroplanes do have protection e.g Airbus but not until speed has bled off to about Vls (B777??). Earlier a/c had no such protection. If the speed loss is significant and automatics are not recovering then pilot intervention is a must. And so it is very important to know when capturing (ALT*) or when maintaining (ALT) a target altitude.
For an extreme example look at A330 crash at Toulouse during test flight 1994
A330 Crash Toulouse
Many factors involved but its this feature which sealed their fate even though they recognised it and monitored it, they delayed too long (FCU set to 2,000 ft with simulated engine failure and very very early ALT*)