A raised rear during stroking can be part of an individual cat's response to touch, but it is not a universal invitation to continue or press harder. Read the rest of the body and the context. A relaxed cat that stays nearby is different from one becoming tense, flicking its tail or turning sharply towards your hand. Keep contact brief and pause to see whether it asks for more. Some cats enjoy touch near the back, while others find that area sensitive.
Do not assume a behaviour that looks amusing is harmless if it is new or associated with pain, excessive licking or skin irritation. Ask your vet about unusual changes. Respecting the cat's response helps you learn its preferences without turning a simple stroke into an interaction it feels unable to end. Try a brief pause with your hand still: voluntary re-approach provides more useful feedback than continuing because one body movement looked positive.
For product comparisons alongside this advice, see Velvet Nest and Sterling Court litter tray. The details below explain their sizes and uses.
Further reading: cats.org.uk; cats.org.uk; cats.org.uk; scottishspca.org.
Velvet Nest
Sterling Court litter tray
Taj-MeowHall