We present ongoing work to understand and formalise notions of “readability” in diagrammatic proofs and to use these results to extend an existing Euler diagram proof system. This work is in its early stages. We outline our intentions to define a theoretical framework, based on an empirical study, that maps users' varying cognitive preferences to corresponding proof strategies. The framework will be used to extend a theorem prover based on Euler diagrams, enabling users of the system to select from among the strategies while constructing proofs.