Do small changes in elevation affect POI?

I was messing around with my Avenger .22 with some JSB 15.89gr this weekend. I zeroed it at 30 yards (doing 850 fps), and noticed that when I switched to a target at 50 yards I had a 1 inch drop in POI. Would a 1 inch drop between 30 and 50 yards be expected? 

I would mention that I'm shooting down from my deck which is about 10 ft above the ground. Where the range is setup there is a slight increase in elevation so that the 30 yard target is about 2-3 feet lower than the 50 yard target. Could this slight increase in elevation in the 50 yard target account for the POI change? And, could the fact I'm shooting slightly angled down be contributing? Thanks!
 
if anything the angle makes it shoot 'higher' .. 30y is probably the most UNideal zero for an airgun possible also ...remember, your sight line is straight and it intersects the arc of the flightpath .. what you want unless just poking a static target, is to set your zero/sightline so it skims the largest portion of the arc possible .. thats where ballistics software comes into play, but yeah, shooting up or down beyond 10 degrees or so can affect poi quite a bit at distance, it will hit high ...