The field guides tell us that Broad-billed is distinguished from female Leaden by the male having more glossy blue upperparts; both sexes having broader, more bow-shaped bills; richer rufous colouration around the throat and breast; and different tail patterns, with Broad-billed having shorter outer tail feathers, giving its tail a more rounded rather than square-shaped appearance. This graduation in the undertail - a "layering"of three or more feathers - is regarded as a particularly salient feature in view of the difficulty of being definitive about other features. It is well-illustrated in the photograph above by Tom Tarrant.
For the discussion here, I am grateful for input from Jeff Davies, Chris Corben, Graeme Chapman and Henry Nix, all of whom have either intricate knowledge of the identification features of the Myiagra flycatchers, or have extensive field experience with Broad-billed.
One of the group of three appeared to have particularly glossy blue upperparts but I failed to photograph it. These three birds behaved very much like a family group; if they were Leadens, it was curious that there was no sign of an adult male. However, it was pointed out that the photographs I posted on my blog of two of the four birds showed the birds did not have graduated undertails so were most unlikely to be Broad-billed. The bird shown above does not have a graduated tail so appears to be a Leaden.