I know how frustrating a tail biter can be, I am at the end of my tether with my boy but he has lots to do and seems happy enough, I now realise why my mother always shouted when I bit my nails haha.
What I have noticed is that recently I had to put my male in the sorority for a few days, dont worry he was divided from them

and as he was distracted he didn't chew himself and his tail started to grow back, also I change the tank around every so often so that he doesn't get bored with the deco, its like us always re-decorating our houses because everything just gets too familiar and boring

Another thing you could try is placing something outside his tank for him to focus on, this is often suggested with glass surfing but I find it works for his little tail biting habit too