There's a LOT to this, but the bottom line is that a bike with a Bolton/KT Systems controller installed IS ADJUSTABLE when it comes to PAS levels.
As noted above
@BKing likes his PAS 1 target speed to be in the teens. My own preference is something under 10 mph, maybe even closer to 6-7mph, so I can easily mix it up with traffic on foot for instance if necessary. This is done using a combination of C5 for bigger changes, then fine tuning using C14. Takes some dinking around making changes and testing them, but they can be dialed in to just about anyone's wishes/speed they have in mind.
On top of this, KT has this thing called "imitation torque control" (see the P3 parameter) that can really smooth things out. No more luching or power tapering depending on your speed. With imitation torque control turned on, speed is no longer a factor. Power will no longer taper at a certain speed (depending on PAS level set). Instead of being speed based, with imitation torque control, the controller uses varying amounts of power, the amount of power depending on PAS level. The amount of this power is set the same way you would set if it were speed based. You use C5 to get you in the ball park, and C14 for fine tuning.
"Imitation torque control" is chinglish for speed based PAS, generally only found in more deluxe controllers. Using this, using the PAS levels, you tell the bike how much assist you want. Could be no assist (PAS=0), or could be just a bit (PAS=1 when set up with 75-150 watts of "assist" or more, exact amount to be determined by YOU). Set like this, the bike can easily be ridden at speeds under 10 mph. As long as the PAS is set to 1 the assist level does not change, no matter how fast you are going. If you'd like more assist, you go to a higher PAS level.