Good question and one I have asked myself.
My antenna is a 2 x 16 meter doublet fed with 11 meter open feeder which enters the house in a
fixed cupboard in the living room. Don't ask why!
The shack is upstairs and RG58 coax is run through the ceiling of the fixed cupboard into a
similar cupboard in the upstairs room and further to the radio. All in all about 8 - 10 meter
Talking about convenient, walking downstairs upstairs at every band change is not.
I tried a rf-sensing remote auto-tuner downstairs, but at times it got stuck and required to
be used on a different band first, before it settled at the band of interest.
I am using a 1:4 balun between the auto-tuner and open feeder.
The next thing I did was to compare on all bands 80 to 10 m the antenna current in the open
1. the auto-tuner downstairs and 30 cm RG58 between the tuner and balun.
2. the auto-tuner upstairs next to the radio and 8 - 10 meter coax between tuner and balun.
(Which took quite a bit of upstairs downstairs.)
Much to my surprise and against common theory, the antenna current did not show a signicant
difference on any of the 9 bands used upstairs or downstairs.
My current auto-tuner is a Z-100 plus, located next to the radio and it works.