Different AMI lineages offer different answers. My own lineage advocates for adult-size chair(s) on the periphery; others have no designated space or furniture for the adults. Each has plausible rationales. For the ‘real answer’, look at the role of adults in the child-centered Montessori Prepared Environment. The adult’s mandate is to promote independence, without being a distraction. This goal can be met regardless how the adults position themselves; and conversely, an adult can be a distraction from either vantage point. It’s not the furniture – it’s how each adult acts to fulfil their Montessori role that is most important.