The two more damage multipliers on the top right of the runic invocation skill tree do not seem to function. Regardless of the amount or types of runes consumed, the damage does not change. I posted a short video below showcasing the bug in action. The video only shows two invocations, but it seems like these nodes do not work on any invocation. It is easy to see this with DOT invocations.
This could explain why many people find the damage for Runic Invocation to be somewhat lackluster.