Since switching to the Harrows Magnums in early November I've need to make changes to the stems and flights to get the balance right.
I noticed with the Short stems that the balance just wasn't right, and I'm now using Medium stems. This corrected the feel of the darts as I threw them, but it then became apparent the the Pear shaped flights were no longer giving enough “lift”. I therefore changed from Pears to Standard. They are the Ruthless Xtra Strong Poly type, which cost marginally more than normal (40p instead of 30p), but are far more durable and keep their shape far better than the old Poly Plains I was using.
I'm also using stem grip springs, and they seem to hold the flights far tighter in the stem, so I no longer need to continually push the flights down into the stem.