[Klaus]

Not taking any field curvature into account, indeed focussing at the horizon/infinity/main subject gives the best results.

 

http://www.trenholm.org/hmmerk/DOFR.html

 

He's talking about maximizing the depth-of-field which is a different discussion compared to critically sharp foreground corners.

 

In an ultra-wide image I find sharp foreground corners to be paramount - thus where you see object details - whereas I can live with a somewhat less sharp infinity region which is blurred by the atmosphere anyway - thus where the details are reduced anyway.

 

Your mileage may vary.