Use a t-square to set your nocking point but you must be sure the timing is set correctly on the bow before you even begin.
1/2in high is just a starting point for you, with a split finger release you might get it to shoot at 1/2in high but 3-under will require more nock height and would not be suprised if you had to go 3/4in nock high or more. Also finger pressure on the string can affect it as well. If you put alot of pressure on your ring finger then the nock pt needs to be a little higher. Have to release the same way everytime.
Since a low nock position will cause the nock end of the arrow to kick or launch off the rest I would suggest going up to 1in nock high and then start working your way down. Never start out low and work up, always start very high and work your way down.
Nock low on the string will cause excessive contact with the rest and can give you a L or R kick in your arrow as well, so start very high and work down and you should be able to get it. Good luck!