A RAW value is essentially made up of the bits that you turn on and off. In global.h you'll see the config_t structure. Inside that you will see:
iac_conf; // iac, bit7:softidle bit6:asym bit5:dualsol bit4=1:ignadv ON, bit3:preciseidle bit2:stepper(0=pwm) bit1:tps_follow bit0:power_iac_only_when_move
Which may help you understand why the value changes when you select the different features.
Rob