I have found that I get a lot of rice hulls at the end of grist-in even when adding them throughout the process though the auger. I believe it is because my Grist case has a severe cone (60%) and the heavier grains "rat hole" though to the bottom. If you have a similar setup you may want to add them by hand into the tun as you grist-in.
I am curious to hear what "problems adding too much" zbrew2k had. I use 3 lg ice scoopers per bag- appx. 10% of grist