Als ik jou was zou ik voor een riem gaan die over de gehele lengte 10cm is.
Het doel van een riem is dat het druk zet tegen de buik zodat je je buikspieren harder aan kan spannen en dus je onderrug beter wordt ondersteunt.
Het is dus niet logisch om een riem dan een kleiner oppervlak aan de voorkant te geven, zulke riemen zijn slecht ontworpen door mensen die er geen benul van hebben.

Edit: Source:
"A properly designed and adjusted belt is useful as a safety
device when you’re squatting heavy weights. A belt protects the spine by increasing the amount of pressure that
can be applied to it by the muscles that support it. The belt itself reinforces the “cylinder” of the ab muscles
around the spine. At the same time, the belt acts as a proprioceptive cue for a harder abdominal muscle
contraction: you can actually squeeze harder with a belt on than you can without one, just as you can push harder
against a loaded barbell than you can against a broomstick. This effect ultimately produces both stronger abs, due
to the stronger isometric contraction facilitated by the belt, and a stronger squat, due to the heavier loads made
possible by the more stable spine.

A properly designed belt is the same width, usually 4 inches, all the way around. Many millions of cheap,
junky belts have been produced with 2-inch buckles and fronts, and either 4- or 6-inch backs. These belts were
designed by someone who did not understand how a belt works. For the belt to function correctly, it must act
around the complete circle, and there is no reason for it to be wider in the back than in the front. Four inches is
about the widest belt that most people can get between their ribs and hips. If you’re shorter, or short-waisted, you
may need to find a 3-inch belt. Thickness is important in that a very thick, laminated suede belt feels very good
under a big weight. Its almost complete lack of stretch makes for a comfortable ride. Such belts are expensive,
though, and any good single-ply 4-inch leather belt with a good buckle will suffice. Even a well-made Velcro belt
is still better than no belt."
- Starting Strength 3rd Ed. p.91-92, -Mark Rippetoe

Ik denk dat de bewegingsvrijheid van zo'n smallere riem meer opweegt tegen de steun van een bredere riem. Youri heeft me ooit geleerd om zo'n cheap belts om te draaien en het bredere stuk vanvoor te gebruiken, het zijn immers je abs die veel oppervlakte moeten hebben om ergens tegen te duwen.

Tekst kwam allemaal van DBB ergens.