When  they  count  the  speed  aura  and  they  are  the  same  speed,  the  champion  with  the  higher  base  speed  will  go  first  due  to  recieving  the  aura.

Likewise,  if  two  champions  have  the  exact  same  speed  counting  aura,  sets,  buffs,  and  masteries,  then  the  champion  in  the  higher  position  will  go  first.

Higher  Accuracy  means  a  greater  chance  of  landing  your  debuff,  so  you  always  want  your  accuracy  have  a  good  gap  between  the  enemies  resistance.

Even  if  you  have  higher  Accuracy,  your  devuffs  still  can  be  resisted.  Put  as  much  distance  between  the  enemy's  Resistance  as  possible.

Lastly,  even  if  you  have  1000  Accuracy  and  the  opponent  has  0  Resistance,  there  is  always  a  3%  base  chance  of  an  enemy  resisting  a  debuff.

To add, High Khatun has a base speed of 104, while Elhain has a base speed of 107.  The speed aura applies to the base speed of the champion.  This means that even if both of these champions had the same speed prior to battle, the speed aura would be different for both.

For example, assuming you are using HK's speed aura of 19%:

HK's base speed of 104 * 19% = +19.76 speed to her total speed in the game

Elhain base speed of 107 * 19% = +20.33 speed to her total speed in the game

Ohh I see thx to both of u.