Generally speaking, false nock high for a split finger shooter is caused by downward pressure of your index finger on the arrow shaft. This causes a downward bend in the arrow at full draw, which rebounds up when the arrow is shot. The remedy is to draw straight back on the arrow rather than at an upward angle. Your string elbow could be too high, or you could be drawing with your arms rather than your back.
If you are happy with your shooting, and don't want to change anything, just set the nock point high enough that you're sure the nock high is true nock high and not caused by deflection of the arrow shaft. Probably 5/8" for a split finger shooter should do it.