I've long held that 50% mitigation should the exception, not the rule.
I'd have something like 10% reduction for each of
Mitigating factors on-pitch
Immediate apology / remorse on pitch
Guilty plea with apology and remorse (this only counts at all if apology / remorse was shown at the time)
Clean record
Obviously accidental
Equally the opposite of these factors should all increase the sentence by 15%
I also regularly suggest that if any appeal is lodged, then all sentence reductions shold be removed; and only the additions allowed (if unsuccessful in appeal)
On this specific incident, I haven't actually seen it, so I can't judge; but if it was as deliberate as it sounds (here and elsewhere) then it should absolutely be a high-end entry point