Welcome to the community, Padawan,

The reason that the duty cycle plays no important role e.g. in this forum, is that it really hardly matters. Almost all of modern consumer electronics use a demodulating chip, for example [Link: vishay.com]. This chip removes both modulation frequency and duty cycle. Cf, the wavelength of the IR light. (Having said that, I have somewhere heard of a protocol which used variable duty cycle to signal battery state of the sender.) By lowering the duty cycle you save some sending energy, sacrificing some range and reliability. As alternative, you can just lower the sending current.

Information on a duty cycle is simply not present in the Pronto HEX form, just like wavelength...

@mdavej: The IRP form according to John Fine and the Graham's document you linked to, does not allow specifying the duty cycle either. However, it is contained in my extensions to the IRP ([Link: harctoolbox.org]) although at least presently not really used.