In this pic wave 4 is between the 38% the 50% RT which is a frequently hit correction target. I don't get why they would illustrate a guideline of wave 4 span, when a wave 2 can retrace anything between 23 and 99.9% and the 50 and 62% RT are the MOST frequently hit targets.
But OK, I guess this is another way to combine fib ratios with support and resistance levels.