Somehow, at least to me, they would find more use if they belonged to the bottom category.
The Side Blade
Compare with Bottom Accessory Cat Tailand Wolver Tail, and Back Accessories Vita Kit, Wings or Dragon Wings.
It doesn't really fit with either, but when in doubt I'd see it more as a bottom item.
Also, there are fewer Bottom Items than Back ones, moving them to bottom would make more space for other expensive things.
Only problem I see, would be Items that already have a parrying Blade and another bottom item - through leaving them as they are wouldn't hurt anyone either.
It's just something that I wanted to have said, through it's nothing world changing.
The only reason the two sections were split is so that Chroma could have wings for the Chinese New Year promo, despite not having a back accessory slot. Tails go in the bottom slot because they are attached to your hiney. This also gave Bombers a space to put tails on their armor instead of being left out.
I'm neither for or against this.