It's a tricky business to assess a print just after it is made to know if it is right for the intended location. My way is to just have the print around for at least a few days, or a week or so to give it a fair appraisal: in a backed clear wrap (to keep the dust off) propped up by my desk or in another part of the house. That way I'm either happy with it or know what to do to improve it, because I've lived with it a bit and the initial feeling of wanting it to be right has been tempered.
This is for mounted and framed work for clients, general sale or for the home. It's a luxury I never had when I was a more busy professional, but one I take now that my work is, usually, of a less time stringent nature.
Considering the changing light levels of any location through a day, it's virtually impossible to tailor a print to a location that doesn't have a constant viewing light, it's just personal choice to choose a print of your taste for a suitable area.
I understand you questioning the horizontal versus vertical viewing impression because it could be that the angle of reflectance may tend to make the print look lighter when layed flat.
As a solution, it could be that you are overdeveloping the print enough to dim some of the tones, or change the paper grade (harder for a bit more 'snap' or softer to open up the shadows). Just some thoughts,
Mark Walker.