Gitlab-runner (docker-machine) concurency and request-concurency?

Can anyone tell me how to set on gitlab-runner ( docker-machine ) parameters:

concurency (cannot be set from CLI)


Is --request-concurrency same as concurency parm but just for docker-machine executor ?

I would like to have 2 idle nodes, 3 parallel jobs per node and max limit of nodes 10.

I am getting WARN message:
WARNING: Specified limit (10) larger then current concurrent limit (1). Concurrent limit will not be enlarged.


EDIT: concurency should be number of cores + 1 ? and also concurency=request-concurrency ?