That's almost correct: second is direct drive but with correct adjustment so the shoulder of the shift rod is level with the axle end, then first is 4.7mm tighter, and third is 9.5mm looser on the shifter but basically slack cable. As long as the second-to-first pull is near enough, any shifter that slackens far enough will select third. In theory, a SRAM 7-speed indexed shifter will do it (pulling 4.5mm each click), with 3 or 4 positions at one end unused, but who knows why anyone ever would! I don't know what the pulls are on SA 4-speed shifters.
