nRF52840DK Layout

Dear Nordic Teams : 

I find the structure of 50 ohm trace for BLE RF.

The left structure(no.1) is from the reference DK layout and the right structure (no.2) is suggested by out vendor.

I find your trace reference ground is layer4 ( bottom) and the inner layer (layer 2 & layer 3) empty area is quite larger than trace width (10+30+10 mils)

Could you share the reason why you do that and the advantage/disadvantage?