ShowerBuddy SCOC Seat cushion overlay, SB6

I thought this seat cushion would go on top of the of the regular Shower Buddy (SB) with the insert in place but there's a bump in the middle of this cushion that juts out when the insert is still in the chair.

When you place this seat cushion onto the SB chair without the insert, the cushion is not sturdy enough to hold the user up since there's a huge hole where the insert was. Logically, I know I won't fall through since this cushion is too large to fall through the hole in the SB. But it droops a lot and does not feel stable. It is similar to sitting on a very old couch with no support in the center.

The solution I've found is to put the insert in upside down so there's a gap for the bump on the cushion. However, this is not a perfect solution since the insert can still fall out pretty easily.

I should point out that my SB is not like the one in their sample photos. It is the version with the full opening where the seat is like a U shaped (rather than having the closed front). This cushion likely works well with the SB seats like they have in the sample photos.