thanissaro says it's ultimately problematic to remain at one point of focus in doing anapanasati. however, if we meditate on one point long enough then full body awareness naturally arises. it might not be the most efficient method (i think it is commentary inspired when teachers strongly suggest staying at one point). thanissaro doesn't think we should adhere to techniques rigidly, but rather explore and see how different approaches work for us. once one has facility in mindfulness of sensations, i think using one point serves as a sort of anchor and doesn't necessarily lead to the exclusion of the other sensations. even thanissaro's full-body techniques pass over or try to relieve unpleasant sensations (so that we can have full body ease pleasure as a gateway to deeper samadhi). method 2 is what is taught to new people at wat metta: http://www.accesstoinsight.org/lib/thai/lee/inmind.html
. but sometimes we just need to drill the mind in with easier objects (e.g. buddho, or one point).