I save more grass than many, but I cake & grass as long as I can.  Some years until calving, other years, if there is less to pick, I will feed half, and let them pick half until calving.  When I feed, I unroll sorgum bales.  When calving gets going, I will feed enough hay to keep them full, and enough cake to keep them milking adequatly.  It seems too much cake will encourage enterotoxemia.  Too much protein before calving seems to encourage big calves.  When I use bale rings, I use the Tombstone (tapered) feeders.  They are lots better than a straight sided ring.  I've wondered about the cone??  They may be alright.  Different years require different plans.