The mini filter is for the breather from the back of the head on the strainer, the best solution is actually to put it into a breather thank then onto the mini filter, as it will occasionally drip a small amount of oil otherwise.
Kits that take it back into the inlet obviously "solve" this problem but bare in mind they do so by putting it into the intake tract which isnt ideal, especially on a high miles engine as it lowers the octane rating of the intake charge as a result (the standard inlet suffers from this also).