The stoma position relative to our clothing waistband is different for us all. It may be above, below, or nearly inline which can make some dimensions crucial.
Attachment must be comfortable and secure to fill and carry about 10 fl oz, or 300 ml, or about 1/2 lb and practice helps.
Distance between the device's stoma cut-out and its pouch connection point can affect pouch folding when that point is too near the waistband, and, folding can be critical with an ileostomy.
That distance is shown as n.