Ostomy Trials . . .
The stoma seal to barrier can leak onto your skin beneath the barrier, which is felt but may not be visible. That is skin irritation in hiding.

▪︎The 1-piece device means the pouch removal includes the barrier, and preferred by the experienced when stoma access is not required as often.

▪︎The 2-piece approach is common for the beginner, or, when nurse or aide is doing that maintenance. Initially you, the doctor, or the hospital may require repeatable stoma + pouch access while leaving the barrier in place.

The 2-piece device molded flange is a part of its barrier which remains attached to your skin. That may be re-attached several times to pouches, after cleaning out its grooves. The barrier skin adhesives are left alone.
Important to note, a molded flange type retains fluids around the stoma base, which will fully submerge that area. When lying down, that barrier is horizontal which helps fluids penetrate the stoma seal, and not drain out the usual exit.
The ileostomy develops fluids that must be kept off your skin, 8 - 10 pH is painful.
REMEMBER, the barrier adhesive allows showers, and many allow swimming. You must dry these off when leaving shower/pool and note the skin adhesive does Not quit with water alone.
Use a "Remover Wipe" to release.

That teaspoon measurement is from flange diameter and height, minus the stoma space.  A 50mm flange with a 25mm stoma holds 2 teaspoons.
The #10504 is just one example of the type flange with every 2-piece brand tried, except this no-flange version shown next.
Coloplast #10504  2-piece
Pre-Cut 1" (25mm) stoma
SenSura Mio Click Barrier
Pouch Side

Coloplast #10551
After 1" Cut Out


Coloplast #12262
Not Resealable
Body Side
Coloplast #10551 Flat
2-piece, Cut-to-Fit
This is a Coloplast 2-piece system, using #10551 barrier with #12262 pouch. It doesn't have a gap that collects fluids.

6 × 7 × 38mm donut
around stoma
4.5ml Liquid (1 teaspoon)
can not drain when Horizontal
Ileostomy brings fluids which can make a leak.  The higher alkalinity lowers viscosity. It more easily seeps under barrier and is trapped, painfully contacting your skin and forcing a barrier replacement.

Patrick Mullins