The dimensions of every Tycho Magnetic Anomaly discovered are in the precise ratio of 1:4:9, the squares of the first three integers. Lego bricks are not cubes. The standard unit has a ratio of 5:5:6. A scaled down Lego Magnetic Anomaly (LMA) would be 7 1/2 units high but there are no 1/2 height pieces. Flat Lego pieces are 1/3 height. I find coupling 7 standard 1×4 bricks with 2 flat 1×4 pieces to be the most geometrically sound.
This results in an LMA with a ratio of 1:4:9.2, or 5:20:46 in simplest form, which is dimensionally perfect in the Lego realm.
Why not scale it up by a factor of 2, making it 2x8 at the base and 15 bricks high? That’s exactly the 1:4:9 ratio (taking into account the 6/5 height/width ratio). Admittedly you need four times as many pieces, but 2x8s are a standard (if slightly rare) brick, and you can get either two 2x4 or two 1x8 tiles for the top of the monolith.
Oh, the other problem with a larger monolith? It’s a bit out of scale with a minifigure. Ah well.