Scoring double differential cross sections

1- As explained in readme, in Hadr03, hadronic interactions are registered alone. There are no electromagnetic processes nor geometrical limitations. Therefore the size of the unique step of the incident particle is governed by hadronic cross sections.
In your case, you measure something related to the interaction length of ionisation process.

2- Anyway, you cannot get the interaction length of a given channel : this information does not exist !
Step length is sampled on the basic of total protonInelastic cross section. Then, the final state (eg. a given channel) is chosen at end of step.