I leave a couple of feet between the front of my Miata or Wrangler and the next car ahead. I've been driving since the late 70s and this is the first I've heard of the "botton of the tires" rule of thumb. It wasn't taught back in the day (is it, widely, now?) and it doesn't make much sense to me since it's a function of the size and the shape and height of one's vehicle, which can vary greatly, whereas I know where my front bumper is and I can (usually) clearly see where the rear of the car in front of me is, and hence create the appropriate gap. Sure, I might leave more space if I'm on a steep hill and think the person in front might have a manual (another Miata for example) but that's rare.
Up until very recently people seemed to always keep just a couple of feet between cars at stops like I did. This business of "a car length or two" seems like a very new thing - the past 5 years mostly - and that led me to think it's some kind of stupid new internet cancer. Probably some "influencer" telling his/her audience that you should put your dominance on display at stoplights by pissing people off and preventing them from getting through intersections. Or putting your dominance and alpha-hood on display by blocking them from getting into the turn lane at all. Anything to get attention, anything to show that you're not (truly) a nobody, even when you are, because you have power!
I've only been rear-ended once in 45 years of driving. Being a d*ck on the road in order to (allegedly) absolutely f-ing MAXIMIZE your own self-perceived "safety" (from highly unlikely events) at the expense of everyone else is a totally modern-American sort of thing to do I guess. But I'm not doing it.