EnergyStored.High is triggered only if the energe storage is full.
EnergyStored.Low is triggered as long as the energe storage is not full.

I think it is caused by diving two ints to get the percentage of stored energy.
https://github.com/BuildCraft/BuildCraft/blob/6.5.x/common/buildcraft/core/statements/TriggerEnergy.java#L68