[COLOR="#300090"]I've crocheted a Tam but haven't knit one, but the crochet slip has no ease or stretch to it unless the yarn itself has stretch.
Since it is a rib stitch, I would recommend using the front post sc in the knit rib and the back post sc in the purl rib. Use a smaller hook size to tighten the gauge.
Alternatively you can pick up stitches from the top edge of the "hat band" on the inside of the tam and sc/dc around in a one size smaller gauge. An SC or DC on the top, inner edge of that ribbing wouldn't show.
--Jack :guyknitting: [/COLOR]