The X2 Expansion Tube Facility at the University of Queensland utilises a free-piston driver to create a high temperature, high pressure driver gas to propel a strong shock wave. Through a series of shock and expansion processes, an expansion tube generates a high-enthalpy gas flow for testing over a re-entry model. Investigating the facility’s limitations at higher volumetric compression ratios is critical to the study of higher-enthalpy entry conditions, particularly for ice giant planetary entry. Experiments were performed with compression ratios 70 and 82 and were compared to existing ratios 20, 30, and 40. The shock speeds observed for compression ratios 40 and 70 are comparable—despite a higher compression ratio. For a compression ratio of 82, a negative impact on the shock speed is observed. It is proposed that the shock tube’s shock speed may be constrained by inherent limitations in the facility for high compression ratios. Finally, it is theorised that an optimal compression ratio exists between 40 and 82.