All,
There are 3 theories to Magnetic Reel Tuning, 1. slow reel few magnets, 2.fast reel loads of magnets & 3 Medium reel couple of Magnets.
Now I've tried 2 and wasted plenty of mono and I'm talking kilos (1kilo = 2.2lb) here not just a couple of spools. Yes the odd cast went a country mile but the crack-off ratio was just too great. 1 cast in 6 completed.
I then tried the ultra slow reel with 120wt oil and 2 mags (ultra mag size) the reel when flipped in the hand would make about 3 complete turns. This setup was the bizz, you could hit the thing as hard as you like and the line wouldn't lift and you didn't even have to stop the reel at the end of the cast, only down size was loss of distance.
My preferred setup is to use 0-40w with 4 mags set N-S-N-S at 90° to each other, the pitch of the thread on the screw is 4 turns per 10mm (sorry not a tech on pitch types/sizes), I can on a good day getaway with 3/4 turn off. Those who have seen my reels know that they have a positive stop so the mags cannot be wound onto the spool face, these allow a small gap (0.01mm) between mags and spool.
The biggest thing to have is confidence in that your reel tuning won't let you down. There is little to no point in executing your best casting style if the line is going to part with the sinker 50yds down the field.
Slower reels = greater confidence.
Food for Thought

A quick test for you all to try, take a sheet of paper and place it on a flat surface, draw a line 90° from one the side closest to you approx 1" long and 4" from the left had side edge. Place 1 of your magnets, so that it just touches the line. Take a small screw driver (must be attratced to a magnet) and move it slowly from the left habd edge, keep moving it slowly until the magnet moves towards the screwdriver. Make a mark and measure the distance between the new mark and the line. You will probably find that that distance is greater than the distance between the spool face and the insdie of the reel sideplate. So when you have the mags inside your reel thay are acting on your spool even when fully wound off
Trial and error will find the optimum reel setting for you, expect to use a bit of mono on the way.
Led.