Use AS number of smallest prefix, not largest
When looking at AS numbers, Onionoo reports the largest subnet's AS number whereas BGP uses the smallest subnet's AS for routing purposes.
Take for instance this relay: https://metrics.torproject.org/rs.html#details/4E9796481C1E75F75D57E8C1FC8C8ED111433316
It appears to be hosted on AS11404.
It is hosted on Wave Broadband's subsidiary "CondoInternet" (branded "Wave G") which uses AS54858. We should report this instead as this is what's used in BGP.
This could also apply to networks which have a prefix from an ISP but have their own ASN.
Disclaimer: I had Wave in the past and this was also true with my relays, but moved and chose a different ISP (Google Fiber/Webpass) so I can't use an example with my relay.