Is there a standard location?
In any piano concerto that I remember, the soloist was to the right of the conductor.
In a recent cello concerto, the soloist was also to the right of the conductor and hence near the other cellos.
I am trying to remember violin concertos. I am less sure but I think that the soloist was to the left of the conductor and hence near the other violins.
Next week, I will see Mozart's Clarinet Concerto live for the first time. I don't know where the soloist will be.
(Right and left here are from the audience's point of view.)