Is focus variance a normal thing between two similar cameras? (Sony A7III )

[Tor]

This is my first post, so be gentle ;) 

Reason for my questions is as follows. 
Me and my better half both recently switch from Fuji to Sony A7III (autofocus was a huge improvement and we both are on the firmware 4.00) 

But my camera doesn't focus quite as good in dimmer light as hers using AFC.  
Actually it start to struggle quite bad @ F.8 and upwards , and my better half's cameras works under same condition just fine up towards F16 

Cameras are setup identical, Focus AF-c, Zone Focus selected, AFS Tracking speed set to "3", face and eye af is on.   
So if her camera is on F8, I need to be on F7.1 to get similar snap on focus without any hunting
Her camera @ F22 focus faster and more accurate then mine @ F13 

For what I understand the Sony goes to contrast based  focus points  @ F 11 
So It can't be that.

For the test I used two  Zeiss 55 mm f 1.8  and I switched the lens between the two A7III to eliminate the lens. 

In AF-S the cameras seem to be about equal, as the lens then focus wide open before stepping to selected F stop when pressing the shutter. 

I just can't get the thought out of my head that this "issue" might carry over when shooting in good normal lighting as well. Only a bit harder to catch.