Nice one JG,
Are you using a small prussik loop? Dats what it looks like 2 me.....if so, its a good idea to offset the knotted area where the double fishermans knot is so that it don't get caught in your biner then suddenly slip giving you a nasty wee jolt when climbing out on a limb.
When you set the prussik on your lifeline instead of holding the double fishermans in your hand then putting it through, move the knot round so it is asymmetrical, so when it is finally set there is no chance of the double Fm sitting directly in your biner.