Personally I find that crossing limbs impedes flow of energy. Some feel that the discipline of the Lotus asana overcomes this and point out that the perineum may have closer proximity to the flow from Mother Earth or ground but a Yoga instructor told me that sitting with the back against the wall in a corner would bring a better result. I personally like the throne and Thoth asana. Bardon , the author of the classic Initiation into Hermetics recommended the chair or throne asana. I feel that the spine is best relaxed but straight and the feet should be bare and the arms should be supported on the arms of a chair.