What determines the level requirements for Glyph slots?

I’m working on a server that is level capped at 60, and want to alter the level requirements of the Glyph slots to match the new cap, as two of the six slots are locked behind level requirements that cannot be reached at my set cap. However, I can’t find any documentation anywhere on what determines the level requirements for each glyph slot. The glyph DBCs seem to hold information on the slots that do exist, and what can fill them, but nothing seems to be there for their level requirements. Is it hard-coded and requires a core edit, or is there a database or DBC that needs editing to do what I’d like?