need advise to use pellet and slug

hi guys
i have a artemis pr900w(diana stormrider) and scope discovery FFP 4-16x44.
i was happy with my gun and shoot in my home with 18 grain pellets.(10 yards)
i zero my scope and enjoy shoots.
as you can see i made my second barrel band ;D
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my shoot accuracy is 1.5cm for 10 shots.(air pressure start from 200 bar drop to 120bar and empty shots between real shots)
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and everything was fine until i want to test slug !

after 2 weeks daily training with Pellets and shoot hole in hole i got my Slugs and start shoot them.

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i tried different air pressures but nothing channged.

always my slugs hit above my aim.
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and i noticed this:
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distance between Pellet hit and Slug his is same as barrel center and scope center.

now my logic says if i use slug for long range i can hit targets without change scope and for short range i must only use pellets.

but i think maybe there is a better way to use pellets and slugs in same time.

i appreciate any adivise and experiment.
sorry for my bad english :D