Fuzzing a target that takes multiple files as inputs

I have a target that I've compiled with `hfuzz-g++` that takes 4 files as input `target file1 file2 file3 file4`.
I've tried passing these files using `-s` and even tried putting them into a single file and using `___FILE___`.
However, I'm unable to make the program crash.

Is this mode possible with honggfuzz, if not, are there any tips for making this work?