Final answer:
The ratio of fixed to variable costs does not affect the nature of rivalry among existing firms in an industry. Instead, the number of firms, industry growth, and access to distribution and relationships are the key factors affecting competition.
Step-by-step explanation:
The question at hand involves understanding the factors that influence the nature of rivalry among existing firms within an industry. The factor that does not affect the nature of rivalry among existing firms is the ratio of fixed to variable costs. This ratio pertains to a company's internal cost structure rather than its competitive position in the market. On the other hand, factors such as the number of firms in the industry and their relative size, industry growth, and access to channels of distribution and relationships directly influence how much market power each firm possesses, the similarity of products among firms, the difficulty for new firms to enter the industry, and whether firms compete on price, advertising, or other product differences. These aspects collectively contribute to the dynamic of competition within the market.