I've never read her or anywhere of the need to change the flipper power away from the default.
If the ball isn't making the cross the ramp and into the Katana lock, the problem is likely just a less-than-true shot. If the game is pitched right (not more than 7-degrees), a clean shot to the cross ramp will reach the Katana - either to be locked or for a pass-through.
If your game has lots of plays and hasn't been serviced, a flipper rebuild could reclaim some flipper power. New sleeves, stops, and plungers, as well as return springs and bushings, always liven up flippers.
Lastly, there are rejections from the cross ramp that will drain SDTM, but the ball needs just the right amount of pace to do it. A slow rejection will likely fall to the right flipper; a fast one to the left. It needs to be just right to drain SDTM - and therefore, thankfully, it's uncommon. It can't really be adjusted out of the game. If your game is level, right to left, and the pitch is at or near 7-degrees, the risk is always going to be there. I think expecting to save the ball with a deft nudge, the instant it rolls to the edge of that cross-ramp ballguide, is wishful thinking. You're probably better off trying a tip slide (taking a warning in the process). A tip slide (aka tip nudge) is a drastic SDTM save involving raising a flipper and sliding the machine left or right an inch or two to actually bring the flipper tip into the path of the ball to nudge it to the opposite flipper.