Busbar Support Distance and Short Circuit Currents

is there any theoretical calculation for the change in short circuit capacity of the busbar when we make a change in the placement of the busbar supports..

for eg in cubic modular systems the cu busbar dimension s 2- 10x20.

if the support distance is 1 module (192mm) then SC capacity s 50ka for 1s

if the support distance is 2 module then SC capacity s 30ka for 1s.