Yo need to find out what is stopping it going lower.
It might be the damper rod length, this can be checked by putting a cable tie around the damper rod and driving up the road.
When you return remove the damper/spring and measure the cable tie height. Push the damper fully in and measure again, the difference between the two is the available travel in the damper rod.
If there is little or no difference it is already on the bump stops.