I don’t think it is quite that simple. Assist apparently will provide tiny gentle corrections sometimes well before you get to the line, with more significant corrections when you are closer. Whereas “warn” tends to wait until you hit the line or get close. The threshold is not the same (which really is not surprising of course).
You’d really just have to experiment with it to see what I mean.
When I have warn on I don’t get activation at all. With assist it is not uncommon to get a very gentle assist (not to be confused with corrections, which can be quite a bit more obvious). At least, that is my impression of how it works. It seems to have evolved a bit so saying how it “is” is a moving target.