(Typo: min not max! I do that every dang time.)
My first reaction was “oh, wow, why the heck didn’t we go with the positive formulation??” but then I went spelunking and found the reason: we didn’t like how adding more edge-skatey goals would improve your metric.
I’m not at all sure whether that’s a valid objection though! Maybe it’s a bit like an ice cream truck loophole. Realistically you’re not going to be tempted to dispatch your “get more safety buffer” meta goal by creating a new Beeminder goal. Unless you want a new goal anyway, in which case, so bee it? 
Let me repeat that in a new top-level post, along with reviewing the current definition of Urgency Load and posing the question of whether Total Buffer might be better:
https://forum.beeminder.com/t/is-total-buffer-a-better-metric-than-urgency-load/10935
That way we can stay on topic in this thread about custom widgets!