Aluminum sled runner height wrt slot depth, and sled length wrt runners purchased

I have a TS with an aluminum top. The aluminum slot width is 3 phase. It is not accurate, nor is the double-T runner, but the center of the 3 widths is about 5/8" and I could use that as my width for a piece of hardwood as a runner. The top width is only a couple of pinchers at the table surface height along the runner travel. The double T design helps the riding alignment of the low quality manufacture. The runner is held down in the slot, when sitting flat, there is a gap between the runners top edge, and the tables surface, maybe .050" above. When I tug it upward I can just get both surfaces co-planar.
But I am looking into getting another mitre guage assembly from the manufacturer. Canadian Tire. The length is 13-3/4" What can I deduce about the entire front to rear fence distance of design of my sled to be if I were to use this length runner 13-3/4"? There is 7" from the front edge of my table to the beginning of the blade. What is this, or any rule about runner length to design into a sled?
Another alternative is to grind the pinchers back (the runners in orig. mitre assembly would still be held down, and side to side would not suffer)., and use the 5/8" as a hardwood runner width.
I have read all but the ala links under the message "table saw sled" and still can't figure out how high to make runners. I know it says to wax your sled, but should it be sitting on the TS surface, and the runners floating off the bottom of the slot, or is there a trick?
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