ILI's dominant function is Si+ and IEI's dominant function is Fe+. ILI can compromise with Fe+ but he/she cannot compromise with Si+, and IEI can compromise with Si+ but he/she cannot compromise with Fe+. That is why Si+ (Fe+) and Fe+ (Si+) look so different.
'Generally, children with more advanced theory of mind abilities display more advanced social skills, greater adaptability to new situations, and greater cooperation with others. As a result, these children are typically well-liked. However, “children may use their mind-reading abilities to manipulate, outwit, tease, or trick their peers”.'
Fe is definitely related to theory of mind. But ILI usually doesn't manipulate people, so why is Fe+ a conscious (or strong) function? I think ILI's Fe+ is passive and he/she is aware of manipulative people.
"The second peculiarity: the contents of vital track functions is the result of individual period of psyche development, the period when we are individuals, when we are the hub of the universe, when everything rotates around us, around our interests, when we are still children and we are not interested in the society with all its demands. Socionists say: the vital track is the superblock of individual life activity. This means that vital track functions work for our individual needs and in the way that is customary and comfortable for us."
This could be another reason why ILI's Fe+ is different from IEI's Fe+. ILI's Fe+, Fi-, Se+ and Si- would be "individual functions".
Here's yet another explanation.
All functions can lead, so IEI does not play tennis (for example) with a leading Fe+. But some functions can more easily become leading functions.
Si+ and auxiliary functions (Fe+, Se- and Fi-)
Se- and auxiliary functions (Fi-, Si+ and Fe+)
Fi+ and auxiliary functions (Se+, Fe- and Si-)
Fe- and aux...
Si- and aux...
Se+ and aux...
Fi- and aux...
Fe+ and aux...
... or the strong functions can lead:
Si+ (Fe+) Se- (Fi-) ... ego
Fi+ (Se+) Fe- (Si-) ... super-ego
Se+ (Fi+) Si- (Fe-)
Fe+ (Si+) Fi- (Se-)