Ostomy Trials . . .
Stoma's position near waistline sets some dimensions for devices. Types may change in time, but our priorities remain:
* Prevent Leakage,
* Make Attachment Comfortable,
* Extend Time Between Removals.

        Details to help select:
▪︎Waistband + Stoma + Clothing
▪︎Above, Below, or Inline w/belt
▪︎On a Fat Roll or, in Dip Between
▪︎Bend Waist Without Leaking
▪︎Side to Sleep On, Hang Pouch

Distance between stoma cut-out and pouch affect pouch folding. A wrinkle in this area can allow liquid seepage beneath the barrier, and that may hurt based on pH even though it's in hiding.

See A Few Samples:  

Good Fit   touch it
Coloplast #10472
Flat, Pre-Cut 1"
ConvaTec #416725
Flat, Pre-Cut 1"
Hollister #8925
Flat, Pre-Cut 1"
Coloplast #10551
2-piece Flat,
Coloplast #16731
Convex, Pre-Cut 1"
Hollister #8662
Convex, Pre-Cut 1"
Some manufacturers use a color code along with a barrier size code. Example shows a Coloplast barrier with a dot tells its millimeters & color code. Their #10551 cut-to-fit shown here is 35mm barrier, and GREEN. When that part became a 25mm Pre-Cut, the barrier went to 40mm and color code remained Green. This can change the overall fit while undetected by color code.
When a brand & barrier with your Cut-to-Fit is established, confirm those dimensions are retained when changing either; different versions require testing with an ileostomy.

Some photos aren't exactly the part they claim, and are not to scale.
Pre-cut sizes are specified.   Barrier millimeters will differ by manufacturer, maybe to flange ID, flange OD, to pouch contact area, etc.

Patrick Mullins