POI changes

I have been playing with different moderators. I've noticed that they all cause a POI change to some extent. When installed and working correctly the POI change stays consistent, but still moved. Even going up in size, say a 25 on a 22 cal there is still some change. Is this caused by the unit itself, weight of the unit, or maybe changing the harmonics of the barrel? Maybe Neil will chime in and enlighten us. 
 
T3PRanch and Cliff, thank you very much! I learned a lot and it was a very well done video by Matt.

Some things to think about:

1. I recently switched from tripod to sand bags front and back. Need to try switching back to tripod and evaluate (rifle hold).
2. I would have never thought that changing stocks (overall weight) would make a difference in the POI that much.
3. On my Airwolf I do not have a barrel/bottle band, but all of the new ones come with one from the factory (barrel deflection).

I just purchased a TalonTunes CF bottle for my Daystate and once it arrives I am curious if the reduced weight will make a difference in POI. Also a barrel band may be something I want to add with the new CF bottle installed.

There is a post from a little while back that partially covers this topic: www.airgunnation.com/topic/when-is-a-free-float-barrel-vs-a-supported-barrel-more-beneficial/
 
They are all over. Let me explain a little more. Clipping is eliminated, so forget that. I have a Weihrauch and two sets of the FX stackable. They all move the POI approx 1/2-3/4 of an inch at 50 yards. BUT, once they are installed the POI location stays the same. Still stacks the pellet. Now the weird part. I can change the order of the cups on the FX stackable and alter the POI again. Go figure. For all I know the moderators are having no affect on POI, and it's me changing it by installing them. Maybe I need a girl friend.