First, be sure your requests are really attainable. Are you positive?
If they still aren’t meeting them, ask more.
Sometimes a challenge can be so slight, we ignore it. In that case, we need a larger challenge to attract our attention.
Recently, most of my students were not regularly submitting practice logs for the 5min/5day a week requirement. I had cajoled, begged, praised; nothing was working.
So at the end of one rehearsal, I said, “Clearly your 5 minute practice regimen is not working. So we’re changing it…to 10 minutes.”
Will asking more of them solve their practice problem? Not on its own. But as part of a multi-pronged attack, I think it will.
Asking more lets them know you are serious about the issue. As long as you are not crossing the line into onerous, too-demanding, or simply impossible, asking more is a way to express your values and the values of your ensemble.