Yes, UNLESS you have some ball magic. Example of when it could reach the mini-playfield and NOT have magnets active -
1. Bridge Diverter bounces ball back up ramp, and then on the second pull of the bridge diverter, the ball rolls under it and into the Mini Playfield.
2. Air Balls - Hitting a ball just right, or it bounces off something, etc.
3. Multiball - If you have more than one ball in play, and shoot two up the right ramp, the first one will get tossed by the bridge diverter, and the second could roll under the diverter as it's tossing back the first ball.
Like Fiberdude says - if the magnets SHOULD be on during 'Battle The Power', the main flippers will be deactivated. (During multiball, flippers remain active, obviously.)
If 'Battle The Power' is lit and the ball enters the Mini-PF and the main flippers do not deactivate, then your entrance switch may not be registering all balls correctly.