Yes, I think the percentage is a factor of the total host CPU, not the allocated CPU value, which is what the UI displays.
The Nomad APM plugin in the Autoscaler is pretty bare bones and not really the best for real usage. I would recommended trying to use Prometheus if possible. You can should get the same result from the UI using a query like:
nomad_client_allocs_cpu_total_ticks/nomad_client_allocs_cpu_allocated
You might need to filter by job and group and sum the value for all tasks and allocations.
But I think you make a good point and it’s something we should be able to support in the Nomad target. I went ahead and create an issue in our repo to track this.