User blog comment:Emptylord/Sandbox/Custom Patch Notes/@comment-1330314-20140324195326

I don't think changing mana regeneration to a percentage of mana would be quite a good idea:
 * Mana regen and mana are separate stats to determine a champion's play pattern in lane. Some champions, like, have a terrible mana pool but great relative mana regen, so they can't spam abilities but can get back to full mana fairly quickly. Others, like have a large initial mana pool but terrible regen, so they can assert themselves early on but have to go back to base if they run low on mana. Turning mana regen into a percentage of mana and fixing it so that each champion gets the same initial mana regen would cause high-mana champions to also never run out of mana in the long term, whereas low-mana champions would suffer.
 * Similarly, this means that buying mana items would also implicitly grant mana regen. A mana-based top laner who buys a or an  would also end up getting enough mana regen to not have mana problems if they sit in lane for a long time. It would also make itemization choices confusing: currently, mana regen is the short-term option for solving mana problems and mana regen is the long-term solution, but with this system mana would offer flat mana and mana regen, stepping into the functionality of both stats (even if mana regen items are retuned to be more effective).