It probably depends on how your lo is comfortable, but from day one, I've been putting Grayson on his side to sleep, using a sleep positioner. Now, he is 16 weeks and likes to be so far on his side that he is resting his tummy on one of the cushions of the sleep positioner. This allows his top leg to fall over the bottom leg and it exposes most of his back for the sh-sh-pat. It's true too, you really have to get down to their level to sh-sh properly and do it loud, loud enough that it is over whatever sounds they are making. I can tell that volume matters when we do it. If I'm timid, he keeps fussing, if I do it loud, he calms easier. It's strange to me, but it must mimic the sounds of the womb or something. I wouldn't be albe to sleep with someone yelling sh-sh in my ear, he he. Oh and be careful not to do it right into the ear, make the sounds past the ear so you don't perforate the eardrum.
Jessica