I haven't shot the airguns at 100 yet, but I have been shooting several 22LR at 100 lately, and I have similar groups to yours. My Kidd custom made one hole at 25, and group similar to yours at 100. So I'm still learning.
I have a similar experience with my HW97K, but I'm not shooting paper. I shoot small targets at 30, but suffer about a 45% miss rate 75y.
Cause?
Wind:
Most of the time I can blame wind, because it has been very windy.
Parallax:
I've tested my scopes parallax error and found it's focus and Paralax to be excellent.
Scope Cant:
This one is likley the cause of many of my issues at long range shooting. This became apparent when shooting my HW30 at 75 with a scope that can't make that adjustment. I had to turn the magnification down to 4x to be able to use the last notch in the mill dot reticle. The hold over was about thirty inches! When you know the pellet is going past the center cross and falling down to the point your aiming with, you realize that 1/2 " of can't is a 1" miss, if all other factors are perfect. It would be the same even if the scope could make that adjustment so that you could center aim at 75.
The Gun/ammo, consistency:
Changes in fps, or pellet weights. will affect long range shots. Large deviations would effect the vertical point of impact. So this is my next point to check out.
Other:
With HW30 the pellets were already falling in an arch so that minor changes in range or elevation affected the point of impact. Like shooting at targets on the gound compared to up at target height would change the point of aim in the vertical.
The same long range problems exist on all guns, but are magnified when your shooting at the edge of a guns capabilities.
Fun stuff!