Assumption of a Roche lobe-filling companion implies a mass-radius relation R_c = 0.082 (M_c/0.1 M_⊙)^1/3(P_orb/40 min)^2/3 R_⊙, shown in logarithmic scale for different AMXPs with orbital periods around 40 min. From bottom up, the sources are IGR J17062−6143 (Strohmayer et al. 2018), XTE J1807−294 (Campana et al. 2003), XTE J1751−305 (Papitto et al. 2010), XTE J0929−314 (Galloway et al. 2002), MAXI J0911−655 (Sanna et al. 2017), IGR J16597−3704 (Sanna et al. 2018a), Swift J1756.9–2508 (Krimm et al. 2007b), NGC 6440 X-2 (Altamirano et al. 2010), IGR J17494−3030 (Ng et al. 2021), HETE J1900.1−2455 (Kaaret et al. 2006), IGR J17379−3747 (Sanna et al. 2018b), SAX J1808.4−3658 (Wijnands & van der Klis 1998), and IGR J00291+5934 (Galloway et al. 2005). The magenta dashed lines show the AMXPs with detected type-I X-ray bursts, while the green dashed lines show the AMXPs without type-I X-ray bursts. The red points mark the inclination angle at 60°. We note that from all AMXPs with the orbital period shorter than 1 hr, except MAXI J0911−655 and IGR J17494−3030, no type-I X-ray bursts were detected. We also show the mass-radius relations for low mass regime H-poor dwarf equation of states for O (dot-dash lines), C (dotted lines), and He (solid lines) as well as low (10⁴ K, lower lines) or high (3 × 10⁴ K, upper lines) central temperatures.