Set Docker volumes size quota within docker-compose driver opts?

I am testing with docker-compose and volumes storage quotas.

This is the docker-compose.yml I have working for now: Which is pretty much a simple Apache, with PHP and an upload php file.

What I am unable to find is to make the volume be "like the others", I just want to add the quota line, something like this:

volumes:
    storage1:
        driver_opts:
            o: 'size=100000,uid=1000'

    storage2:
        driver_opts:
            o: 'size=1g'

    storage3:
        driver_opts:
            o: 'size=100m'
    ...

...but of course this does not work, I need to specify the device, which I do not know what the default is, and if I need anything else.

Like I said, I just want "default" behaviour with the size quota working, and I though I could achieve this by re-setting the default values in the mandatory driver_opts parameters. So, how could I achieve that? (If there is a better way, please tell me.)

System: Ubuntu 18.04 LTS x86_64 / Docker 18.09

Thanks in advance.