Schematic of emitting regions for previous TW Hya observations, compared with the region probed in this work. For comparison purposes, observed disk structures in millimeter grains (ALMA, Andrews et al. 2016, VLTI, Menu et al. 2014), micron-sized grains (SPHERE, van Boekel et al. 2017), and CO gas (Banzatti & Pontoppidan 2015; Huang et al. 2018) are shown. The vertical scale is not meaningful. References: (a) Dupree et al. (2012), (b) Brickhouse et al. (2010), (c) Herczeg et al. (2002), (d) France et al. (2012), (e) Bergin et al. (2013), (f) Zhang et al. (2013), Bosman & Banzatti (2019), (g) Banzatti & Pontoppidan (2015), Bosman & Banzatti (2019), and (h) Zhang et al. (2017). The “zone” labels correspond to the regions described in the analytic calculation of Sect. 4.1.