Source emission region radii for the GBM sample. The red and orange vertical lines represent the value of this radius for 211211A and 230307A, while the dashed vertical line represents the median value of the distribution. The red shaded regions indicate the values expected by the IS model (10¹³ cm ≲ R ≲10¹⁵ cm; Rees & Meszaros 1994; Daigne & Mochkovitch 1998), while the blue one indicates the expectations for the ICMART model (R ≳ 10¹⁴⁻¹⁵ cm; Zhang & Yan (2011)). In the decade 10^{14 − 15} cm (purple), the two regions overlap, and the emission radii in this region are marginally compatible with both models.