Lots of very small magnets spaced together on material will not mess up the fan above. You can check by waving a screwdriver above at the height of the carriage. If you can feel the screwdriver pull the magnetic field is too strong and will mess up the fan.
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Depends where you place the magnets
Encasing the magnets in steel will help to redirect the magnetic field away from the head/fan. My magnets were disrupting the fan until I shielded them.
Now, if you place them back to back, there is very little attraction. You can easily pull them apart with two fingers. Face to face is strong enough to be dangerous, though. I have the blood blisters to prove it. 
Using non-magnetic material like wood or plastic around a magnet, while attractive, does nothing to redirect the magnetic field.
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I speak from long hard experience. I had no thought that the magnets could be the problem but noticed that the fan became stuck and unstuck by what I thought was gunk in the fan and went through a lot of trouble to keep it clean. I also noticed that whenever the smoke became flame it would not cut as deep and the smoke became flame whenever the fan slowed down.
Once I discovered that the magnets were causing the issue with the fan, my high school physics (college physics not needed for this) kicked in about the relation of electricity, movement and magnetic fields and I realized that while the fan was the highest speed object on the carriage there was an awful lot of electronics there also and the head was moving fast enough to have perhaps subtle effects but not any good ones, and resolved to limit magnetic fields to not being detectable near the head with a lightly held screwdriver.
Knowing how oblivious I was to the effect of the fields, I feel the need to warn others as I wish someone had pointed it out to me sooner.
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I’ll keep it in mind
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Thank you so much for sharing this! I’ll be making some tonight.
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Great project. i have been looking for something like this. Thanks
Doesn’t that strong of a magnet interfere with the laser head? I had purchased some strong neodymium magnets on Amazon, but they were so strong that if they even got close to each other, it’d about snap your fingers off! We ended up using them to hold down vent covers so that our iRobots don’t knock them off!
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