This morning in Shul I sketched a picture of a negiyah between a reish and chof pshuta and showed it to a child, who read it as a lamed (see below).
While I agree the case I posted yesterday was very mild, and not much of a chshash, I think in cetrtain cases a reish / chof pshutah negiya such as the one in this picture below can indeed present more of a problem. Particularly in cheaper mezuzos where not all the letters are written so perfectly.
An especially in sefardi ksav, where lechatchillah the lamed is more like a reish on the bottom than a chof.
Anyway, for this reason, I always like to show anything more than a very thin / light negiyah to a rov for my own peace of mind. Often while they may not be a shinuy tzurah, they may still loose their mehudar status which is tricky esp. when you are wanting to sell the parshiyos as geder mehudar.