For me, it applies to even walking or standing. When walking and conversing, my personal space extends around 20cm around me. When walking without conversing, it becomes about 60cm. When sitting, I generally avoid the person and often find myself stimming after a short time. Regarding choosing seats, I tend to pick corners or edges (especially distant ones) unless all of the seats have been surrounded. In a case like that, I generally shutdown for a while (about a few subjective seconds in most cases) until someone invites me to sit down. There's some indistinct fear of sitting down next to someone else without invitation, but it may be nothing more than my theory of mind with its assumptions about most people encountering the same feelings and thought processes.