Again, a bit of insight from my friend who reports about threats to RAVEC (just a general picture, no specifics).
Part of the particular risks to royals is that their schedules are planned and known about in advance, and that they generally have an element of prestige, plus other royals and VIPs present. Private occasions are not generally known of in advance. This is what the royal household rep shares.
Malicious individuals generally want to make a splash with their attacks. They choose high-status public events as targets and are more competent/organised. Mentally unwell/obsessed ones want to make a personal connection. They are generally impulse-driven and, shall we say, not the sharpest tacks in the box. Castles are easy to protect because, well, they're castles.
Harry shared that his assessment went from 100 to 0 because he withdrew from being a working royal. But if he's not attending public royal events without other royals present he won't be as easy to find, target and attack.
So a threat from someone who knows your likely location might plausibly go down if they've much less access to information, or if the location isn't as important/significant to make a statement.
But this computes to Harry as... Well, it doesn't compute.
(My friend only gave a gist on how assessments/threats occur, the rest is my speculation.)