The other thing to remember is that the wood being inserted must be the exact thickness of the kerf and when you clamp up you mustn't overtighten the end clamp else it will break or bend the last millimetre left and you will get broken knots and your crossover measurement won't be correct; you should also tighten up the side clamp at the same time as the end clamp. In theory the clamps should only be tightened up a fraction to prevent the insert and glue combined from moving too much as they settle and dry. However it is tempting to tighten up just that bit more to ensure that the glue is tight!!
PG
After edit My only other comment would be to move the knot up a bit toward the top so as to retain some proportion, ie 2/3 blank below and top 1/3 containing the knot. Otherwise there isn't too much wrong there.
