The difference between Stevenson and Lofgren alignments lies in the fact that the Stevenson alignment uses, as an input to the Lofgren formulae, the inner recorded radius when solving for the nulls. In other words for IEC, 60.325mm (for DIN, 57.5mm).
In effect, what is happening is that the two nulls that result are the nulls that would be the case for a record with an inner recorded radius of 54.806mm and IEC/DIN outer of 146.05mm.
There are still three maxima for distortion, but only two are within the playing area of an IEC LP.
Interestingly, Rega arms are noted for their non typical alignment, and can sometimes be difficult to set to LofgrenA/ Baerwald IEC without altering the mounting distance. Many use Stevenson for their Regas, with nulls at 60.3 and 117.4, as opposed to Rega's 60 and 114.
However, for those with Rega arms interested in experimenting with another alternative, a nice alignment can be had setting up with nulls at around 63/64mm and 109/110. This keeps the original mounting distance of 222mm, with only the offset angle reducing slightly from 22 degrees to around 21.4, and overhang increasing minimally from the original 15mm, by less than 0.4mm, if at all. These radii will give less distortion on the inner 2/3 than Stevenson, without the problem of not being able to slide the cartridge to get Lofgren A or B.
