One of the many valuable things I learned from Alan Flusser’s Dressing the Man is that better suspenders are sold in sizes. As with waistcoats and cummerbunds (which were also sized in the past), I’ve come to realize that “one size fits all” really means “one size makes do”. Such accessories accommodate obese men by using long buckled straps that on other men become an abundance of excess material. In the case of suspenders men have to accommodate this excess by hoisting the shiny metal clasps up to their chest where they are much more likely to be visible. Even for gentlemen polite enough to keep their dinner jackets on throughout the evening, if they’re not wearing a waistcoat then the upper portion of the braces will inevitably peek out at some point.
The good news is that this distraction can be minimized by having non-sized suspenders altered to remove the redundant fabric which in turn allows the clasp to be properly (and discreetly) positioned down near the waistline. The clasp, in turn, can then be hidden entirely by a cummerbund or waistcoat which will also conceal the suspender ends.
Another trick to minimize brace exposure is to use white dress suspenders, a perfectly correct option for black tie. In the case of white dinner jackets this is really the only option if black suspenders will show through the coat’s unlined fabric.
On a related note, I normally recommend Albert Thurston for sized evening braces as they’re the only company I know of that still makes them. But when I checked their web site today I discovered that even they have now reverted to a single “multifit” size. (Sigh.)