My Domino's (I've the 500) slip tenon joints are consistently tight and I like them that way. The only time I've run into difficulty due to the tight fit was the first time when I applied glue to both the mortise and the tenon, and the piston fit and excess glue caused the wood to split. I then did a series of tests, with different thicknesses of tenons, different species of wood, glue on the mortise only, then in the tenon, only, and on both the tenon and in the mortise. The one consistent thing I came away with was that if the mortise was too close to the surface of the wood (or approximately closer than 3/16") then splitting would occur when glue was applied to both the tenon and inside the mortise.