How well do the GXP novels sell?

[Ryo-Okay]

I was on Amazon Japan and I saw GXP 15 was the bestselling title under the Fujimi Fantasia Bunko label. It's even outselling Rokudenashi Majutsu Koushi to Akashic Records which has an anime airing right now, so I was wondering how well they sell.

[Dr.Soviet]

If I recall right the physical copies generally sell out at major book stores, not sure about online.