ccminer vs excavator difficulty

[Staller]

Hi, miners,

I mine equihash on Nvidia 1070 and i tried two miners ccminer & excavator.
And i have noticed that for the same target from the pool ccminer and excavator have different difficulty:

for example, i got target 0000400000000000000000000000000000000000000000000000000000000000 from the pool
ccminer says it is 1023.94 diff, but excavator says 15420.2

I tried to found out why, and found how to calculate diff for ccminer, but could not found anything about excavator.

The question is why there is a difference?

Tnx!