Taxidermist, is the ice you are fishing snow covered? I'm guessing it's not, if you are concerned that your shanty is causing a shadow. If you are fishing on clear ice with no snow, then these fish can definitely detect that you are there especially if you aren't quiet and happen to be wearing a blaze orange hunting suit!!!! Now, if the ice is snow covered at all simply clear enough snow for just your shanty, set it up, and re-pack the snow around it to cut down on light penetration. Then close all windows and doors to block as much light as you possibly can. If you need light, set your lantern in the back of your shanty, not between your holes. Perch, expecially monsters like you describe, are generally always on the bottom, and are sight feeders. Sometimes, fishing 2 poles with waxies on one, and a minnow on the other will clue you into what they prefer to eat. One little trick my grandpa taught me, is to cut 2 holes. In one hole you fish with a bottom slammer rig only. Simply clamp your lead depthfinder to a hook and bounce it off the bottom for 30 seconds every now and then. This stirs up the bottom real good, and usually gets even the most finicky perch to start a feeding frenzy for himself and the rest of the school. This works especially well in crystal clear water like you describe, because the fish can sense it and see it from a greater distance, and will come running to not miss out on an easy meal. Just some pointers man, I don't mean to preach, and I realize that you are probably already doing some of this stuff, I just thought I'd share some of my experience with you. Show me some pics of those 15 inchers when you catch them!!!!!!!! Good luck, and tight lines............