Do keep in mind that what we define as the threshold is different from that of a microdose. The threshold is the point in which the substance produces a set of effects that can be taken as representative or scalable to the common response, the point in which the distinct characteristics of the substance becomes apparent. LSD and ALD52 at the microdose ranges do not meet this criteria, and can essentially be seen as different kinds of substances. For example, the dopaminergic and noradrenergic aspects predominate at sub-threshold ranges, whereas the threshold is the point in which the serotonergic activity becomes apparent.
In any case, I think you're right in that 50ug for the upper end of threshold is too high, but I also think 10-20ug is too low and in the microdose range. I changed it to 40ug and will consider lowering it if we get more reports that it's off, but as far as we know, this is the best current representation of the average response as derived from the sum of reports available on this substance.