Unable to vary QMax in batch mode using Electron-Photon EPA

Dear Experts,

I am computing \gamma \gamma \rightarrow \mu+ \mu- at an electron collider using the Equivalent Photon Approximation (EPA), which is a part of the default PDF library. The EPA structure functions run like
\log(Q^2/Cutoff^2) + polynomial terms
and the parameter used to fix Q in CalcHEP is "|Q|max".

In the Batch Mode, I am finding that "|Q|max" must be set explicitly to a number and cannot be set to a varying parameter, e.g., half the invariant mass of the mu-mu system, M(m,M). The error codes returned are
cs.o: ERROR in strfun
cs.out: CH Error 2

Ultimately, I would like to scan over "|Q|max" and quantify the scale variation. This is certainly possible for the factorization/renormalization scales in hadron collider pdfs. However in my case, as a first step, CH would need to recognize a symbolic expression for "|Q|max". I am wondering if it possible to extend this feature to initial-state photons from leptons.

Thank you,
Richard