There's been a lot of discussion about this on Pinside. I ran a search on "mode hole" in the IJ thread and here are the results I've found:

https://pinside.com/pinball/forum/topic/ij-williams-you-cheat-dr-jones-club?tq=mode+hole&tu

I'm telling you as a super-fanboy of IJ that taking out the scoop entirely and lining the area around the back and sides with dead drop foam from Pinbits is absolutely the best way to get close to 100% assurance of the ball sticking in the hole. If you want to play with all the other things people have experimented, be my guest. You'll eventually come back to my fix.

Run a search in topics and posts...lots of stuff on this problem.

Get yourself a bunch of this (I usually buy 5 strips at a time just to have them on hand). Look around on their site...they have some other cool stuff:

http://www.pinbits.com/index.php?main_page=product_info&products_id=131

You've got to half-disassemble the POA playfield to get under there, remove the plastic, and the scoop. Put the scoop somewhere safe; you won't need it anymore. Line the back and about an inch of the sides with the strip of dead drop foam (not too much on the right side...it shouldn't hang over the edge of the hole too much - if it does, you used too much). Before you put the plastic and playfield back on, you can test it out by firing a ball in there with your hand. Should be pretty consistent sticking in there.

Any questions, give me a holler.