The LTE Event A1 is triggered when the serving cell becomes better than a threshold. The event is triggered when the following condition is true:
MEAsserv - Hyst > Threshold
Triggering of the event is subsequently cancelled when the following condition is true:
MEAsserv + Hyst < Threshold
The hysteresis can be configured with a value between 0 and 30 dB.
As per my knowledge there is impact of UE power in serving cell measurement but dont know the detail :(