The square base of this pyramid is bulges in an attractive curve simply because of the geometry of the balls. The third row from the top has a slight discontinuity due to corner effects.
The method will not work on small pyramids because the outside surface tends to skin off because of those same corner effects. The square base needs to be about 10 or 11 magnets to a side, preferably more.
![](https://i.ytimg.com/vi/10xghne4MHU/maxresdefault.jpg)