Has to agree with “2 houses in a mainstream neighborhood is better than 1 house in a hot neighborhood” since that is what I did in Singapore.
But not so sure about 6 houses in a questionable neighborhood (from context is not in a desirable neighborhood) than 1 house in desirable neighborhood.
The issue is not about ratio. Is about the sustainability of rent in desirability neighborhood, the risk exposure (e.g. robbery, eviction, vacancy rate) in a questionable neighborhood, other hidden costs that are omitted in the computation of cap rate and cash flow, and overall return of investment.