Sometimes you may want a thin pulse width, and you may notice after dialing in a pulse width of 0-1 or 98-99 some keys appear dead or the sound is barely there.
At extreme pulse widths, there will be a voice -to–voice and a frequency dependent variation. When really thin, the analog electronics are just not going to be perfect. This is especially true on the upper end of the range around 95-99, where there may be some fluctuation of the pulse width signal. Calibrating the filter can get them as close as they're going to get.
If a thin pulse is desired, use the low range of the keyboard, where voice-to-voice consistency is much better. If it were perfect (i.e. digital), a pulse width of 99 is the same as 1, just inverted, so it sounds the same and either value can be substituted.