In Nebraska we can only have 1x (non-magnifying) scopes on muzzleloaders, so when I saw a TC 1x scope for sale, I bought it and put it on my new inline.

Now, I'm not too sure of the correct physics terms of this, but when I peer down the lens, moving my head slightly will "move" the crosshairs significantly -- without moving the barrel.

How do I make this consistent? (One way I discovered was to remove the scope and use the open sights, but I'd like to find another way.)

Thanks in advance.