When sniping an Evie who is about to leave Ice Block, aim a little bit in front of her path in the direction she's facing because she will usually blink after leaving the block and tends to walk forward a bit first.
Learn how to bunnyhop and you can hop out when sniping the enemy Sha Lin across the map. It would confuse him seeing you flying up in the air and lunging across the map a pretty far distance. Learn how here: https://youtu.be/2rYToy5eUas?t=315