That's the whole trick. Good code makes complex stuff look simple. Bad code makes simple stuff look complex.
The compression would presumably remove the redundancy of the language itself as a factor (including differences in idiomatic cyclomatic-complexity "depths" of various stdlibs), and also remove any redundancy in the way the test cases were specified. So it'd be down to a measure of how much circumlocution and over-engineering you did in the process of implementing the solution.
I'd worry slightly that code-golf solutions would be rewarded, though. Maybe pass everything through an obfuscator + linter before computing the metric, so that things like identifier lengths and spaces aren't considered.