Why the separation is twice times of the trace width?

For difference offset Coplanar strips,
If the trace width W1 is 60um.
Option1: S1=120um, D1=120um, then get Zdiff=90.99 ohms.
Option2: S1=300um, D1=300um, then get Zdiff=98.93 ohms.
Someone said that S1 and D1 should better be twice times of W1. So he denied option2.
I think option2 is feasible, who can give comments on that?

This is used in mobile phone, that is multi-layer board.
I don't think there would be some difference for two options in EMC, EMI, etc.
What's your idea?
Thank you very much.

- - - Updated - - -

This is used in mobile phone, that is multi-layer board.
I don't think there would be some difference for two options in EMC, EMI, etc.
What's your idea?
Thank you very much.