My bath doesn’t have a shower rail or curtain, but it does have a shower head.
What I like to do is combine both the shower and the bath. So, I’ll sit in the bath while rinsing myself with the shower head, then let it rest between the legs while applying shower gel/shampoo, which gives you a bit of a hot tub sensation around the gooch area.
After the shampoo has done its thing, I’ll rinse and then just allow the submerged shower head to continue to fill the bath, at which point it gets switched off while I lay back and bathe.