Thresh and Relic Shield

So when i play , i start with . Relic shield stats that it executes minions below 200 hp. When i aa a minnion to execute it, it doesnt execute. I can still get the heal for me and my adc if i actually kill it but i have to try to cs. So when my adc needs hp in a fight and i try to get us some hp, i have to tell them "Hold up, i gotta get some farm" XD. So it really makes it hard to get the hp back. The point of the item is to get quick hp without really needing to remove yourself from a fight. Just wondering if its just me or what is happening. Well, thanks for reading. Have a nice day bbs. =D