I don't see any problem with the removal of the shelf--or making the anchor well deeper and removing the foam.
If you are worried about dragging--especially if you are mostly anchoring in Florida waters, you have plenty of line--in the PNW--you should have closer to 300 feet. I probably would increase the chain.
Please understand that the Brait stows in less area, and coils better than the double braid, and that is why I make an issue of the specific line.
http://www.yalecordage.com/pdf/anchoring_tech.pdf
When I initially posted, I found a site which showed New England Ropes made an 8 strand braid--after further checking I am not so sure--so I suggest the Yale Cordage. The 8 strand can be spliced. I have also splices a 12 strand braid.
Also what anchor do you have? If I was worried about dragging, I would be looking at the Manson Supreme or Ronca anchors. I carry a Delta 14" and three 7# Fortress anchors in my 22. I have plenty of room for 150 feet of 1/2" 3 strand nylon-and carry another 150 feet of back up 1/2". But I also carry 3 more sets of chain and rode for the Fortress anchors. One of these is 3/8, the other are 5/16" line. These are stern anchors or back up bow anchors.
I have anchored more times than I can count but well over the several thousand thru the years. I have rarely drug anchor. When I have it was either the anchor was not appropriate for the bottom--such as a CQR in mud, I fouled something, such as picking up a mason jar on the tip of a Delta anchor--or into a log, or in what I call "Ball bearing" bottom--where the bottom was nothing but a thick layer of rocks about 2" to 4" in diameter successful anchoring means the right amount of chain, scope, proper anchor for the bottom and technique. Anchoring can be an art--and has to be approached slowly--I like to set the anchor by hand, feel how it is gripping the bottom, as I let out scope--when it seems set, then apply reverse to set it in. If it fails--then move--and try another part of the harbor--but look at what is on the anchor as you bring it up. There is no one perfect anchor--I carried 3 on the bow of my long distance cruising boats (over kill for a C Dory) but one plow, one Danforth HT and one Fisherman with long sharp spikes for grass or weed.