Form is a difficult topic with contemporary music (as the term seems to be used in the UK, as opposed to modern). As developments broke with tradition those traditional forms were eroded or abandoned leaving composers to work out things for themselves – if they found it necessary.
To me, it’s feasible for the form of a contemporary work to be unique, a one-off, especially with through-composed works where proportion and episode are more relevant than traditional structural components. It isn’t saying that a contemporary work shouldn’t fit a traditional form just that it’s less likely to – and may actually be formless beyond its internal logistics – how the material is drawn together.
On setting out on a new composition the last thing on my mind is its formal construction. However, proportion and contour (particularly in dynamics and timbre) are very to the front along with how well motifs can be exploited.