Your right on a couple of fronts-- I'm not sure of what I am doing, and the more you raise the shaft the more the rocker tip will move out toward the exhaust.
But, there are a few things that I am much more comfortable with after doing some math and mockups.

I have four different rocker arms (Isky ductile 1.5, Crane Gold 1.6, CAT 1.7 and Harland 1.6-Mancini), three lengths of pushrods, lots of rocker shims and a full day of mock ups.

So here is what I found in my day of mock-ups.
The rocker you use can make a substantial difference in the amount of shim that is required and the amount you have to move the shaft back as you raise it. It can also determine how much change in lift you will see from the pushrod side. It looks like the primary factors are 1) how far down your shaft currently sits in relation to the valve tip, it is a little tricky but you can measure it (I wound up making a little fixture that sat on the valve). 2) How long your rocker arm is and how big the roller on the rocker is, 3) cam lift. You can calculate your theoretical adjustment from this info.

In my case, the +.150 and no offset was from the standpoint that my shaft was about .200 too low (valve to mid-point of shaft) and I moved from a CAT 1.7 to the Crane 1.6. The Crane is shorter in length and has a much smaller roller than the CAT (Harland copy), which 1) greatly reduces the need for the shaft to go up and 2) moves the roller tip back toward the intake on the valve. Now the downside to the Crane is the oil hole, it requires you to have a couple of threads showing on the adjuster to properly oil the pushrod cup. When you have to extend the adjuster you are increasing the "kick-out" of the pushrod (this is why you want to use the longest pushrod your can), so it decreases the vertical movement (valve lift). In my case, I lost over .030 in valve lift. I could get back some of the lift from relocating the oil hole and use one of my longer pushrods, or use the Harland (oil position is much higher) but because its longer and has a larger roller, it would require +.250 in height (moving the roller tip even more forward), and a new longer pushrod, an offset spacer and hold down. It would also mean grinding the shafts and clearance to the head for the pushrod to go back. Now, the Crane set up worked out great for me, as one set of my pushrods was the exact correct length with the two threads showing. Now is the rocker tip exactly at the center of the valve, nope but it is in the middle third. It is my understanding that the scrub distance is more important than the location to an extent. Just for reference my .130 scrub with the CAT rockers was perfectly centered, heck it almost had to be as I was using 35% of the available real estate, so I am going to call my middle third good.

This has gotten me to about 90% of the calculated perfect, so I feel like I have picked up a little understanding in this process, enough that I probably will not ever run an engine with a .130 scrub again.