AMC1100: Surge immunity difference between AMC1200 and AMC1100

Hi team,

I have one question about surge immunity test of AMC1200 and AMC1100.

on AMC1200 datasheet Viosm is 6kV.

and for AMC1100 Viosm is 4615V. but Vtest is 6kV. 

1, these Viosm means same specification? why Vtest =1.3 Viosm?

2. if no, what is the difference?

best regards,
Takuya