Look at this link from above :
Many things come into play while using VST’s live. You are going from a stereo setting to mono, which in some cases will give you either right or left sounds only. It is really dependant on the way your setup produces sound. If there is a mono setup for Ravenscroft, I would use that. It also would be best to take off all effects, then slowly add some back in, to taste, in mono. Read all of the above comments, which could be of some help to you. There are many here that use Ravenscroft, maybe they will chime in, but there are many more piano VST’s available. I have found in my experience, according to type of gig, that a simple, less sampled piano, and less effects works better, especially in mono.