There's an 'Agent Availability' measure with the following description: Agent Availability aggregating equally named agents per host. I believe this will do what you are looking for. In the details tab for the measure, you can filter by agent group. If you are charting it, you can split by agent host. Have you tried this?
Thanks Kayan. I attempted your suggestion and noticed that when charting the measure sometimes I got the correct value. Other times the measure gave double the correct value. We saw this same behavior with the Connected Agents measure.