Best washer configuration for shroud?

I’m making a 1.5″ dia. shroud for a custom 16.5″ barrel. I have 5.5″ of open interior space available in front of the muzzle and a 20″ overall shroud length. What would be the best washer spacing for the available 5.5″ space? Some people have said to vary the spacing for harmonics, if so should the size vary from big to small (how big, how small) or better staggered randomly? Or, should I just space them equally to get the biggest chambers like the milled cores posted here in other threads? Are fewer big chambers better than a lot of small ones? Also, how close should I locate the first washer from the end of the muzzle if I’m using vented barrel bushings? Has anyone done a equal comparison between a spaced washer design and a milled core? If the milled piece was far superior for some reason I might just make one of those instead. By the way, it’s a .25 cal custom that I was hoping to get to 110 ft/lbs so I’m going to need a way to shut this thing up if I want to use it in my back yard. My .177 is a little small for the coons.