There is some personal preference on this, but keep in mind that the longest channel for the project is best. Bidwell recommends using channel that leaves 3-4” from the end of the wood, this way it is generally out of the way of hands, and out of view. An example in this situation would be a 44” slab would use a 36” channel, leaving 4” on each end. Although lots of our customers like to run 1.5-2” from the edge and in this example a 44” slab would use a 40” Channel.