All the algorithms were designed to take this situation into account. I don't remember the exact nature of each, but most process the inputs as stereo and either sum the wet outputs (the dry signal is summed to mono). There may be a one or two instances where this isn't exactly true, but we made the most musical decsions in those cases. I can dig deeper if you want more specifics, but for now just know that we planned for this situation.
The only thing that's undefined is using input 2 and not the appropriate mono input 1.