This is how mana regeneration works now in Dragon Realms.  You regenerate a % of your remaining mana, so it is advised to not drop below 70% or so for the largest mana regenerating pulses.  Below a certain % of available mana, there is a minimum regeneration that will set in.  (With 0 harness, even 10% regeneration would be 0 mana, so they put in a minimum regeneration per pulse).
 

 

MAGIC PRIMARY
0 - 200 ranks 4%
200 - 400 ranks 4.25%
400 - 600 ranks 4.50%
600 - 800 ranks 4.75%
800+ 5%

MAGIC SECONDARY
0 - 400 ranks 4%
400 - 800 ranks 4.25%
800+ 4.5%

MAGIC TERTIARY
- Flat 4%


* Clerics have a bonus to this rate above and beyond other guilds.