Why should the SQP method use boundary sphere diameter instead of equivalent sphere diameter?

Hello,everyone!
In the SQP method, the diameter of the boundary sphere and the equivalent sphere diameter are not the same. The particle volume calculated based on the bounding diameter is much larger than its equivalent sphere volume. Can the equivalent sphere diameter of non spherical particles be input in the bounding diameter? Will this affect the calculation results?

The bounding sphere is used as first step in collision checking. If particles are separated from each other (or wall) by at least the diameter if the bounding sphere, then contact is impossible and the more detailed (and slower) checks can be skipped.
The volume-equivalent radius will be too small for this and collisions will be missed, leading to incorrect results.