Upper panel: detached systems in the frequency – characteristic strain plane. Open circle, square, triangle, and diamond show positions of detached sdB+WD binaries PTF J2238+7430, HD265435, CD-30°11223, and OW J0815–3421 respectively. Solid red line shows confusion limit due to binary WD and LISA instrumental noise (Korol et al. 2022). Blue line shows the pre-contact evolutionary track for the system with initial parameters M_He = 0.43 M_⊙, M_WD = 0.87 M_⊙, P_orb = 90 min, placed at d = 1 Kpc. Position of the system at RLOF is marked by an asterisk. Lower panel – semi-detached systems in the frequency – characteristic strain plane. Open circle, square, and diamond show positions of semi-detached sdB+WD systems ZTF J2130+4420, ZTF J2055+4651, J1920-2001. Blue line – continuation of the track shown in the upper panel in semi-detached stage. See the text in Sect. 4.3 for objects references.