WLAN Access Point network is typically optimized for communication scope, and not for localization. It is thus important to understand the positioning accuracy limits under a certain given Access Point topology and to be able to make design recommendations if the Access Point topology can be adapted better for the navigation needs. This paper calculates a Cramér-Rao Lower Bound -based criterion for Received Signal Strength -based positioning. Two study cases are presented about how the proposed criterion can be used to choose the optimal Access Point density and the optimal Access Point topology in a network designed for positioning purposes. In addition, our Cramér-Rao Lower Bound-based criterion can also be used to estimate the expected accuracy bound in an existing network, based on its underlying Access Point density or topology. Measurement-based results are used to verify our proposed approach.