Event-level epsilon is used to compute the channel capacity of a source and obtain a randomized source response. Currently, if a source's event configuration exceeds channel capacity it will be rejected; however, a lower event-level epsilon may be provided during source registration to increase noise and reduce channel capacity to accord with the limit.

The flexible-event utility currently advises on the highest such event-level epsilon. For example:

npm run flexible-event -- -w 1,2,3 -b 4,5,6

advises that by providing event-level epsilon 11.405 (default is 14.0), randomized trigger rate is increased from 0.0072807 to 0.0894337 to accord with the channel capacity limit for navigation sources.

Rather than reject source registrations that exceed channel capacity limits, ARA implementations could default to automating setting such an epsilon on the client, with the ability for consumers to turn it off per registration. This would give API callers a tradeoff between more possible event-level configurations and higher noise.