The biggest advantage of a high pH is in breaking emulsions and keeping some undesirables in solution that would otherwise require filtering. If you add your base gradually and note the pH you will see there is a point where a lot of orange/brown crap precipitates, then as you raise it higher that crap redissolves in the basic water and becomes very black, and then after adding even more base the surface of the solution becomes completely flat and no emulsions can form. Adding too much lye is a waste and can lead to lye in your product so don't go overboard. 50-60g in 150mls H2O is enough for 500g of bark.