We present a post-hoc analysis of a benchmarking activity for information retrieval (IR) in the medical domain to determine if performance for queries with different levels of complexity can be associated with different IR methods or techniques. Our analysis is based on data and runs for Task 3 of the CLEF 2013 eHealth lab, which provided patient queries and a large medical document collection for patient centred medical information retrieval technique development. We categorise the queries based on their complexity, which is defined as the number of medical concepts they contain. We then show how query complexity affects performance of runs submitted to the lab, and provide suggestions for improving retrieval quality for this complex retrieval task and similar IR evaluation tasks.