Some tests and theories associate E with more sociability and I with less of it, whereas with other systems, E and I are made of completely different traits.
One neurologically inspired theory by Hans Eysenck relates E and I with person's preferred level of psychological arousal, associating higher preferred levels with E and lower with I. Person is said to feel greatest comfort level at their preferred level, and rapidly decreasing comfort at any higher level. Sociability is not given any special meaning in this E/I construct.
How much does extraversion equate as sociability to you?