Thresh with the Relic Shield.

Okay, so I have noticed this for a while and thought it was done on purpose to discourage all but the best Thresh's from playing with the Relic Shield, but I'm beginning to thing this isn't the case. I know I have seen this for a while, Thresh's interaction with the Relic Shield and subsequent upgrades can only be described as wonky and hard to use properly. Even with the passive up, I find it hard to actually execute a minion below the required health with an auto attack, often having to resort to other things such as flay or hook. I think(I actually have no conclusive evidence) that the correct way to use the Relic Shield is to move into melee range or something like that as its original intent was to only be used on melee champions, but is there a way this can be fixed to be more interactive with Thresh so that I am not pulling out my hair missing cannon minion cs and annoying a solo que adc who keeps crying telling me to stop helping him cs. I like the item on thresh as it has all the useful stats to build him tanky earlier(the coin has no health whatsoever) but the passive minion execute almost completely discourages me from using it in anything other then an occasional game.