Hmm, that's an interesting question. I feel that it's kind of subjective, because the levels are slightly different for each bike... and some have 3 levels of assist while others have 5 or even 8. Do you wish that level 1 would go slower than 8mph... I feel like this question is most relevant for affordable cadence sensing electric bikes, many of which use the same 12 or 6 magnet disc sensors (exposed or sealed) and those bikes generally have planetary geared hub motors. Many of these ebikes have displays which have settings that allow you to adjust the top speed, but this won't necessarily tune level 1 down proportionally. In short... I guess 8mph is just efficient for the motor and slightly faster than the 4 to 6mph speed of many walk modes.
You can usually enter into a display for an ebike by holding the up and down keys, or plus and minus keys simultaneously, or you can double tap the power button or hold the i button or settings button. Also, walk mode is usually activated by holding the minus or down arrow... some systems have a dedicated walk mode button. I hope this helps! This question is pretty fringe in my opinion, so I'm not planning to make a video response. Thanks for posting though, and I'll check in on any reply you make