The crazy thing is the rule does not protect me from shit.
I'd be at 75%, but as long as the value was plummeting my ratio would go below 75% and I could buy more. But I skirted this line and judged wrong a few times.
But if you buy something for $1 and are at 75% and it appreciates to $100, now you are way above 75% so they step in to "protect you."