I developed a meta-parameter variant tester to automatically find a configuration that does not crash: https://github.com/thesourcerer8/caravel-stdcelllib-stdcells/commit/b3f3487cb9c8bba61f86bb58cf29afe147082437

you might also want to consider taking a look at this: https://github.com/efabless/openlane/blob/master/regression_results/README.md

True, I should have taken a look at it. I thought it's more about numerical optimisation