If it works for you and your gf - those are the 2 most important people you need to please (you and the gf)... kudos!
Dior Homme eh? I have that too and I'd go 4 sprays on the undershirt chest area plus 2 sprays on the unseen underside of the dress shirt's collar. Evaporates slower = lower sillage = lasts all day.
I'm not worried about staining the dress shirt because that's in the area no one except me will ever see. This despite the fact I know my dress shirts are expensive made-to-measure customized down to the last detail. Plus I just refuse to wear perfume on my skin. Reason: Former org chem student.
Tomorrow morning: Prada IdI... 6 sprays on undershirt, 2 sprays on shirt collar....