Buick 2004 Rainier Owner's Manual page 28

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The lap part of the belt should be worn low and snug on
the hips, just touching the thighs. In a crash this applies
force to the strong pelvic bones. And you'd be less likely
to slide under the lap belt. If you slid under it, the belt
would apply force at your abdomen. This could cause
serious or even fatal injuries. The shoulder belt should go
over the shoulder and across the chest. These parts of
the body are best able to take belt restraining forces.
CAUTION:
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You can be seriously hurt if your shoulder
belt is too loose. In a crash, you would move
forward too much, which could increase injury.
The shoulder belt should fit against your body.