Isn't that software feature? My brother has Xperia XA, and it charges fast up to 90 percent, green light on, when slowly builds up till 100. On Sailfish X it charges straight to 100, no slowdowns etc.
Btw, maybe its just my imagination, but if i charge Sailfish X with other (slower) 5V 1000 mA charger, the battery also holds longer.