Correct me Obi if I am wrong, I had noticed this too - there is a flow that comes round the sidepod, in the undercut, then goes inwards across the top of the floor. On the face of it this flow will be tripped up by the longitudinal curved strake that guides the exhaust plume.
Well, it's too obvious for F1 aero engineers not to have noticed lol so either the flows are alright - maybe it's turbulent there from the font wheels?? - or it's a temporary/test solution that will be updated for Melbourne. Be interesting to see if it changes.
Here is a poor MS Paint illustration of what I mean, I think go it however:
The forward part of the strake is curved inwards, allowing the light blue airflow to curl over the top of it and over the exhaust flow, into the coke bottle region and over the diffuser. It could be that the Mercedes fence provides better isolation of the different flows (especially the exhaust plume), but its length prevents the optimum influx of air over the diffuser.
BTW, previously when I stated 'it seems to me (armchair aero engineer) that Mercedes isn't entirely happy with the exhaust flow/plume from the W04.'
, I didn't mean this area of the car was poorly conceived, on the contrary it may work very well, however I was wondering if it was an area Mercedes believe could be improved.