Also plants will probably adjust their growth habit to their growing conditions. There is plenty of room between what they 'characteristically' look like in habit and being etiolated because conditions are too poor to maintain a decent to good looking growth habit. If growing taller gets them more overall surface exposure to the not so harsh light they are getting behind glass on a windowsill then that is a much better proposition for the plants long term survival than staying squat and globose, where a much more limited amount of surface area gets sun exposure and there is less surface to lose moisture. Similarly thinner spines will let more light get to the plant's surface, thicker spines block more light.
