It is obvious from figure2 that, in the mixed case, an increase in A or (and) D decreases v_opt, but an increase in B increases v_opt, i.e. decreases 1/v_opt .
It is obvious from figure2 that, in the mixed case, an increase in A or (and) D decreasesv_opt, but an increase in B increases v_opt, i.e. decreases 1/v_opt .