Mechanics of Elise E spider form

So i have been training a bit of Elise lately ( don' t look at my match history for your well being ) and i got problems with Rappel, the E in spider form. Sometimes it just feels clunky or does not do what i intended to be, and probably i am missing something

So, if i directly target an enemy i jump off rather quickly, descend on the enemy and get the surprise bonus. So far so good.

If i target the ground i go up and i can' t get down on my own unless i target another enemy again or wait the seconds of untargettability, and in the case i do not get the surprise bonus. But there is a time limit for that? Because sometimes when i go up, even if i spam E a half second after going up on an enemy it does not allow me to drop on it, and after the 3-or-so seconds i find myself helplessly in the ground

Also, even the targeting bounds seems off because it does not let me target an enemy at the border but still inside the whole circle, unless that is fault again of the ipothetical aforementioned time limit. I know there were issues in the past where Elise indicator did not match with her intended range, but i barely understood what those were about...

Also, how much time ot takes to be untargettable, or at least there is a significant delay when swapping to spider for a rappel? Sometimes, maybe is my lag or my sloth reflexes, i can' t manage t dodge skills or to clutch rappel away for this reason.