When a die is not compressing enough (low compression index) and the pellets produced tend to be crumbly, the pressure can be increased introducing a tapered inlet to the hole, by increasing the taper depth and angle you increase the pressure. In many cases dies with a large diameter (> 6-7 mm) are made with a large taper depth (15-25 mm depth) to avoid having large die thickness but to secure a strong compressing action anyway.