you cant gurantee in any position of no tearing as it depend on babies position, decent of baby and stretchyness of perineum and control during pushing.

Hands and knees and standing or sitting on loo do lessesn chance due to you positioning and way baby descends down birth cannal and peri.

Best way to facilitate as small a tear as possible is to:
1. suppoerive midwide
2. active birth and position changes
3. sit on loo, stand, or hand and knees for pushing
4 listen to guidance of midwife so that you allow perineum to stretch slowly.

good luck