Funny enough I just managed to find this exact post and comment on google 5 minutes ago when I started wondering whatever it's actually possible to use 1/4 of capacity in SLC mode.

Though what make me wonder is that some reviews of modern SSDs certainly mention that that pSCL is somewhat less than 25% of capacity, like 400GB pSLC cache for 2TB SSD:

https://www.tomshardware.com/pc-components/ssds/crucial-p310...

So you get more like 20% of SLC capacity at least on some SSDs