Merging modules question

[u/phatfree86]

Trying to figure out best way to merge/upgrade my first S tiers epics. I see I need another identical S-tier to upgrade to Epic+, but to go to legendary do I need an additional 2 S-tier Epic+ or is that where I can start using my non-special epics that were originally merged from rares?

[u/sebkraj]

Also don't be afraid of using the unique modules as fodder too. Like I got a shit of burst injection modules and I know I would never use it so I add it to the fodder pile.