Authors: N. Lugaz (UNH), B. Zhuang (UNH), N. Al-Haddad (UNH), S. Banu (UNH)

Large-scale structures are thought to be either radially propagating, like coronal mass ejections (CMEs) and CME-driven shocks, or corotating, like the heliospheric current sheet, fast solar wind streams and stream interaction regions (SIRs). Distinguishing between these different types of propagation is not critical for L1 measurements. However, for future sub-L1 measurements taken from locations closer to the Sun than L1, it will be critical to understand these differences. Here, we use measurements from STEREO-A as it passed sunward of L1 in August 2023 as well as Solar Orbiter as compared to L1 measurements. We show that the best time shifts for spacecraft upstream and east/west of the Sun-Earth line are complex and do not correspond to pure radial propagation or corotating. We discuss these results for space weather forecasting from sub-L1 monitors and for Mars.