There are many factors that could be giving you your sound, material is important because some resonate way better then others. Hang with the tighter grained woods with glass, although Walnut is often considered to be hardwood, it often softens the calls because of the open pore versus closed pore syndrome. As suggested lay two pieces of glass on top of your pedestal and use this as a guide to set your ledge, make it so the top piece of the two is flush with the ledge, this is always a great starting point, remember one thing the closer the top of the sound board to the bottom of the striking surface the faster the sound is going to bounce, making it higher in pitch and sometimes it will rob you of any break. This is another good point about the height of your pedestal, use the 2 glass rule to set up your pedestal height. Now if you are still getting the muffled sound it is the overall depth of your pot, it may be too deep, average is a round 3/4" to 7/8" overall which should give you -1/8" from top of your ledge to the bottom of your pot. The you should have at least another 1/8" to 3/16" thick floor.....you see where this is going? Standard pots make standard sounds, so practice experimenting with the dimensions, you will be surprised how much 1/16" makes. As far as the portal hole in the center bottom...unless you are making dual sided calls, you really don't need one, there are many call makers who have super sweet pots without them, but if you delete this aspect then you have to figure out the exit holes for your sound to come out. I use a eight hole pattern that works for me on my single sided pots, using 3/8" and 1/4" holes alternating. The only thing I know that would make any difference is the O.D. size of your center hole may be robbing from the floor I.D. and make for a dead call. Hope this helps you out some, pappy