achieve certain packing factor / volumefraction_region

Hi there,

I want to achieve a certain packing factor within a given region in my granular bulk material.

I tried to achieve a packing factor of 0.6 (Volume of solid material within the refered region / volume of refered region) within the region reg_ins by using this fix:

fix ins all insert/pack seed 100001 distributiontemplate pdd1 insert_every 1000 overlapcheck yes all_in yes volumefraction_region 0.6 region reg_ins ntry_mc 1000

What happens in the simulation is:
This region ist the lowest part of a cylindrical container. Which means after the first 1000 steps, the particles which have been inserted first, have been settled on the ground and new particles will be inserted until the desired volumefraction_region of 0.6 is reached...
Instead of inserting the new particles on top of the settled particles of the first insertion or in spaces between particles where a new particle would have enough room without touching other particles, the particles are inserted at locations where they have a big overlap with other particles, which makes the particle bed explode...

What do I wrong to reach my desired packing factor of 0,6 in the refered region?

Thanks a lot,
kind regards,

Sebastian