A gain factor is used for calculating one transmit power relative to another transmit power. For example, in UMTS high speed uplink packet access, a gain factor called βed is employed for transmission associated a given enhanced transport format combination indicator (E-TFCI). Conventionally, a gain factor to be used for a given E-TFCI can be determined via interpolation between two of the reference E-TFCIs to reduce signaling overhead. However, certain network configurations may result in one or more of the reference E-TFCIs that could be otherwise be used according to conventional techniques being outside of a valid range. In the event such a sub-optimal configuration occurs, interpolation and/or extrapolation schemes based on at least one reference E-TFCIs that is within and/or or is not within the valid range are used to calculate a gain factor for a given E-TFCI.