Expression text only snaps after dynamic. Should be possible to snap before dynamic.
It seems that the expression text snapping to a dynamic is only considered in the order [Dynamic][Expression text] and not [Expression text][Dynamic]. The checkbox in the Expression text properties reading "Align with preceding dynamic" seems to confirm this.
This surprisingly is not coherent with the Handbook which uses "poco f" as the example, which I can't seem to produce on a score. https://musescore.org/en/handbook/4/dynamics#dynamics-and-text
There are tons of examples where the expression text precedes the dynamic!
Am I missing something? This seems like a pretty strange oversight
Comments
Not knowing what particular dynamic modifier you want to use, I will use your example of poco.
Don't use an "expression" at all, at all. Instead, double-click the f and type "poco" (and a space) before the f. In the Show more under Dynamics, you can select how this longer dynamic marking is centered on the note.