It really depends on how much you trust your stage manager (and how much confidence they have in themselves) in the artistic end of the job.  If the SM is coming from a directorial or acting experience and has added valuable insight throughout the rehearsal process, just leave it in their hands.  Meet with the SM privately if you feel they are not maintain the show to the level you left it.

On the other hand, if your SM is new to the position or has lots of experience in tech and no performance or directing experience, you might want to discuss this issue before you even get into Tech Week.  Maybe when you are polishing or working on interpretation.  Most SM's know when they're not up to it.  Sometimes even perfectly capable SM's would rather have the director give the notes because of a bad relationship between the cast members and the SMs (although we expect good morale and relationships, there are those few shows where the SM is not a good personality match for the cast).

In any case, if you feel that your show is so far off base from what it was opening night--do something about it.  The overall success of a play may affect actors a bit, but it's your reputation on the line as a director.