Setting the toe is often a trial and error case. Measuring the tie bar and prop to prop distance is only accurate to set 0 toe. The geometry of the adjustment is that the angle of the motor is important and it is somewhat easy to determine the required angle if you know the motor spacing and how far back you want the wakes to merge. The distance from the tie bar pivot to the prop center differs by engine, and lower unit. So setting a specific toe by adjusting the difference between tie bar pivot distance and prop shaft distance will differ by engine in many cases. Some manufacturers spec a zero toe and some racing model motors will use a toe in setting. The merging of the wakes in this case adds to stability but does sacrifice performance somewhat since when there is toe out, the thrust is directed at an angle and that causes the hull to turn.
One other thing to keep in mind when adjusting the tie bar. On some tie bar ends where the adjustment is made by screwing the tie rod ball fitting in or out, there is a small hole in the fitting that you need to look at. You should see threads. If not the tie bar end is adjusted too far out nad could break loose under stress. If you can not see threads when you have adjusted your toe out, you need a new longer tie bar or less toe.