MS listening in idle mode BCCH information (serving and neighbors). BCCH TRX is transmitting all the time on max power. Than on BCCH TRX in dedicated mode is RxLevFull equal RxLevSub. For NonBCCH trx it is not true (in case DTX=0). You could see this behavior, if you have TEMS (or similar phone for optimization). Of course this is not 100% true (for example in case of EDGE).