R4 Surf Proper Trim Angle

[cstevenson]

I am hoping someone can help me with my trim question. I have an R4 Surf and when the "Auto Trim" is active the trim stays at -5 and never changes, I have owned many outdrives and try to run the boat at a positive trim but this is my first Forward drive. If I manually trim to 0 the props (feel like
and sound like) start to cavitate. So what I do not know is what is the optimal trim position, is it possible my "Auto Trim" is defective and or not set up correctly and how much trim on an R4 Surf is optimal. Any input would be great, thank you in advance!