As anyone who saw my FX talk at the SE Bash will testify, the OC-2 tracks fine down to at least a Low E. As you go below A, the time it tracks for reduces obviously, but mine all track a low E for about a second before glitching back to just the direct signal. The amount of 'glitch' you get will often depend on how buzzy your frets are, if you have even slightly buzzing, uneven frets, it stands to reason that a pedal will struggle to track that signal. The smoother and rounder the signal you put into it, the pedal will track a lot easier.
Also make sure that your octave goes at the start of your chain, it will again struggle to track a note that effected already.
Si