Schematic highlighting the intrinsic physical models affecting the shape of the Lyα transmission from an example galaxy at z = 9.0, all convolved by the nominal JWST/NIRSpec Prism spectral resolution. The default model with x_HI = 0.5 is shown at the top left, where the grey-shaded region represents the effect of a partly (x_HI = 0.01) to fully neutral (x_HI = 1.0) IGM. For illustrative purposes the expected IGM density field at z = 9 is shown in the top right, extracted from the ASTRAEUS simulations. In the bottom panels are shown the combined effects of the default IGM model and various sizes of the ionized UV bubble (left, blue: R_b = 1,  10,  50 cMpc) and DLAs from local H I gas reservoirs (right, red: N_HI = 10²¹,  10²²,  10²³ cm⁻²). The integration region for D_Lyα is marked by the top line in all the Lyα transmission curve figures and is defined to encapsulate all the predicted physical scenarios.