Cylindrically averaged (2D) 21 cm PS as a function of line-of-sight modes k_∥ and sky-plane modes k_⊥. The colour map shows the PS amplitude calculated from a slice through a single simulated light cone centred at z = 9. The simulation box has a side length of 300 cmpc and was generated with 21cmFASTv3. The blue hashed area is the HERA EoR window. The dashed cyan line is the horizon limit and the solid black line is the horizon limit with a 300 ns buffer added to it to account for additional foreground leakage (see HERA Collaboration 2023). The solid red line is drawn at a value of μ_min = 0.97, where μ_min = cos θ, and $tan\theta =\frac{k_{\perp }}{k_{\Vert }}$. In this paper, we use the red line as a rough approximation for the solid black line.