I have been tracking the lead sources (both inbound and outbound) in a custom field like SEO, PPC - Gooogle, PPC - Facebook, Referrals, Outreach etc.

I would like to get a bit more detailed report on these sources. For example, for inbound leads - it could be Phone call, Email, Live Chat etc. 

It's more like nested sources i.e. SEO lead can call or Email or contact us from Live Chat. But that is not relevant for outbound leads - so having another custom field can be confusing.

How do you recommend to manage these data so we can generate an easy report?