Part of the issue with the higher nock point is the shelf. The ol rule of 1/8" is for an elevated rest. You get great clearance, and you have some "down-give" off most elevated rest so the nock set can be lower IMO.
When shooting off the shelf you have to get the tail of the arrow high enough to clear the shelf without serious deflection. If you set the nock set too low you will get a "deceptive" tune reading. The arrow will bounce and will actually appear tail high, but it is going down then deflecting up.
You have to get the tail high enough to clear the shelf. I start with the nock set high and work down when tuning. In my experience the lower the nock set shooting off the shelf, the more critical the bow is.
If you shoot with one nock set below (split only) then it seems to be lower with the setting for the tune. This is probably because there is nothing to stop the tail from going upwards upon release.
Over the years I have experimented with many differnt settings and always come back to a quate "High" nock set when shooting off the shelf. I really think that a high, one below and above nock set off the shelf is the most accurate and forgiving.
Tiller of the bow can effect where the nock set will wind up once tuned, along with split vs. 3 under.