Primary stellar radii (top) and tidal forcing ratio (bottom) over periastron distances in units of stellar radii (q∕R_*) for heartbeat systems, consisting of the main-sequence star sample from Shporer et al. (2016) (green) and the RGB stars from Beck et al. (2014) (blue). ε Cyg has been added for comparison (orange). Symbol sizes are proportional to the stellar radii. The tidal forcing ratio is calculated as in Eq. (4), and the large errors of the main-sequence stars stem from the high uncertainties on the radii R₁ and the masses M₁ of the primary components. The plot has been created in analogy to Shporer et al. (2016).