Map 6 compares the distributions of the two high vowel mergers before /l/. The red circles indicate the speakers who have completely merged both: there are very few of them, only 11. For 46 speakers, the merger is complete in only one of the two, and these are evenly balanced between the front and back vowels.
The areas in which the completed mergers are concentrated are quite different. As Map 4 showed, the /il/~iyl/ merger is centered in two areas of the South: eastern Tennessee and western North Carolina, and west and central Texas. On the other hand, the merger of /ul/~/uwl/ is focused in a completely different area, the North Midland, concentrated in Pennsylvania and southern Indiana.
These radically different distributions reinforce the initial conclusion that there is no general process of high vowel merger before /l/, but two different mechanisms at work.