Kusto calculated field with Metrics

Question

I’m making a query in Kusto on Azure to bring the value of the Redis memory fragmentation, this value is obtained by dividing the RSS memory by the memory used, the problem is that I am not able to do the calculation using these two different fields because it is necessary to filter the value of the field "Average" of the fields "usedmemoryRss" and "usedmemory" when I do the filter in the extend line the query does not return any value, the code is like this:

AzureMetrics
| extend m1 = Average | where MetricName == "usedmemoryRss" and 
| extend m2 = Average | where MetricName == "usedmemory"
| extend teste = m1 / m2

When I remove Where from the lines it divides the value of each record by itself. Is it possible to do that? Thanks in advance for the help.