Recent work has investigated the resonant dielectric reflectors for high-aspect ratio (AR) imaging and the necessary requirements for index-matching liquids (IMLs) at the prism/sample interface when imaging using a solid immersion Lloyd’s mirror interference lithography (SILMIL) system. These past results showed that SILMIL systems require a prism/IML refractive index (RI) (real component) mismatch less than approximately and an imaginary RI component to achieve good reproducibility and uniformity of high-AR resist structures in the ultrahigh-NA (UHNA) regime without system gapping control. Here, we present simulated and experimental results for an index-matched prism/IML combination and for an IML with an imaginary RI component of . These results present the first SILMIL system that can produce both low- and high-AR resist structures over larger exposure fields than previously reported and without gapping control. We also present simulated and experimental results that show the AR process latitude, which further highlights the improved control compared with previous SILMIL research. Finally, we present simulated results from a materials survey that show new potential candidate dielectric underlayer materials that can accommodate high-AR imaging in the UHNA regime, some of which are better geared for the semiconductor industry.