So nothing specific about displacement, just generalizations about function analysis.Ego sees them as opposites, F is opposite of T, S is opposite of N and I is opposite of E. for example INTP would be able to easily see T and N in the ego even tho they are I/E opposites, because they arent opposite judgments, but J and P, so ego doesent try to repress these, instead it represses opposite judgment, Fe. the reason third is not as repressed by ego than fourth, is that aux doesent have so big of a role in ego(ego sees it less of self than dom), so ego doesent try to repress third as much. and because dom(Ti) is so much of ego 'self' it represses its opposite judgment(Fe) to much greater degree.
Bit naturally this isnt all this simple. because third also works as filter for fourth(like dom to aux), you need to also come conscious of fourth in order to filter it properly. if you dont know what you are filtering, you wont be able to filter it properly. this is why one jungian analyst wrote an essay about third being in the shadow of fourth to journal of analytical psychology.
This sort of mechanisms on the mind(according to jung) extend even out of typology. for example this reconciling third that emerges the union of the opposites(in typology of dom/inferior) can be seen as transference(sort of projection of patients unconscious towards analyst) in therapy sessions, where the opposites would be the patient and analyst. by analyzing this transference will tell about the patients unconscious and this can help the patient to realize more about the self(which is the goal in analytical psychology)