My outlet to field is without d box or manifold. What is with the "left, right, left, etc. dispersing tiles?
A leach field with a distribution box will allow a larger flow rate compared with a single back and forth pipe with no d-box. Peformance of a single back and forth pipe is further impaired if the field is sloped overall from one end to the other because there are uphills in the pipe path. This could pose a problem when large flows occur such as from using several plumbing fixtures and/or the washing machine at the same time.
Stop wasting time re-adjusting the pattern. Have several lawn sprinklers, one for each pattern.