It seems to me that being able to go from the surface to layer 10 is more helpful than needing to make that extra 15 blocks or so that is needed when its only 41
It's only 10 blocks in each direction for CPU's sake. Continously iterating through the whole y-axis (60 blocks up and down from magnetizer) could prove extremely CPU-intensive. As well Magnetizers are cheap and it's nto a big deal to put one every 20 blocks.
