Just an idea,but you could use 3NM using Sha Chau next to CLK,within 40nm of the radar head.Then 5NM with the others for outside 40nm.You wouldn't need MRT sep standards.Or what about the very expensive Precision Approach Radar which is sitting in the corner hatching eggs.
You asked a why??(10 bucks) question about 4NM.Looks like it was a toss up between 5 and 3.Using 3NM down final would get the movement rate up slightly.
