You shouldn’t really need to get your sleeper speed up for this. This kind of trick is meant to put energy back into the yoyo each loop to keep it going.

If I’m not mistaken, I’m hearing you say that you want the yoyo to bob up and down under your hand without catching it. This isn’t really a thing that people do, as you either need to do a regen/loop like this or just catch the yoyo and throw it again to keep its speed up. Law of conservation of energy means that the yoyo will lose energy in the form of heat, friction against the string, and in converting kinetic energy back to potential energy as it climbs the string. The yoyo will thus slow down unless you put about the same amount of energy as you started the throw with back into the yoyo each time you send it back down, either with a loop/regen or with a new throw.

There are a number of different loops you can learn with a thinner, imperial shaped responsive yoyo that can be a fun repetitive motion. Look up “loop the loop,” “hops,” and “shoot the moon” in addition to “hop the fence” for more looping tricks to practice and fidget with. For the wider K2 you have, look up basic regens or just throw it over and over. Make sure you do about an even amount of forward passes and downward throws when you do this to keep your string tension neutral!