Hi Jean,
Use a real dynamic script. These care care of spacing for you.
\version "2.22.1"
psubito =
#(make-dynamic-script #{ \markup { p \normal-text \italic "subito" } #})
{ d'16_\psubito \cresc \repeat unfold 14 d'16 d'\f | }
Maybe I'm going too far in my belief that "standard tasks best should
not require # characters and scheme", but shouldn't we provide a
LilyPond syntax interface for this? It's not so uncommon to want
custom dynamic expressions after all:
dynamic =
#(define-music-function (text) (markup?) (make-dynamic-script text))
{
c\dynamic sfpmf
c\dynamic \markup { \normal-text \italic subito f }
}