people have said that to me, that they stopped zeroing indoors after their POI changed when back outdoors. trouble is, people sit on a bench firing downwards towards a target near the floor and don't take parellax error into account. it's the only explanation ive got because ive never had any problems whatsoever when zeroing indoors. however i have noticed a small spread in group sizes when leaving the door open.
hope this may help you ATB, john
air arms MPR FT .177
wiehrauch HW97 KT .177