The understanding of source code in large-scale software systems poses a challenge for developers. The role of expertise in source code becomes critical for identifying developers accountable for substantial changes. However, in the context of configurable software systems (CSS) using pre-processing and conditional compilation, conventional expertise metrics may encounter limitations due to the non-alignment of variability implementation with the natural module structure. This early research study investigates the distribution of development efforts in CSS, specifically focusing on variable and mandatory code. It also examines the engagement of designated experts with variable code in their assigned files. The findings provide insights into task allocation dynamics and raise questions about the applicability of existing metrics, laying the groundwork for alternative approaches to assess developer expertise in handling variable code. This research aims to contribute to a comprehensive understanding of challenges within CSS, marking initial steps toward advancing the evaluation of expertise in this context.