Rationale for "stacking" black foam on Wound Vac

[oceanblue52]

Currently working home health and doing visits concerning a patient with a pretty deep heel ulcer and a wound vac. It is in a tricky location and one tip I was given from the main nurse managing the case is to tape one piece of black foam down with drape strips around heel, then cut a hole, and then "piggyback" a second piece of foam on top of the first piece before securing with the main drape and track pad. What is the rationale for the second piece of foam? I've dressed it this way and also just with one piece and did not really notice a difference in function. Thoughts for the rationale behind the more seasoned nurse's tip?

[LHRN1210]

Oceanblue: the only reason to stack foam like that is when the wound bed is smaller than the track pad and a larger area is needed (as when there is a small wound or if bridging is required). If a "mushroom cap" or "button" is not made, the track pad can make indentations on skin that is probably already fragile. What brand of NPWT are you using?

[oceanblue52]

I think it is just a KCI? It fits in a little black holder with a flap that lets you access the screen. We never learned about the track pad damaging skin, although that makes sense! It's not a huge wound so I am guessing this is the rationale. Thank you for your insight!