The midpoint between the Ascendant/Midheaven (AS/MC) is about who you are, your self-consciousness, the principle of "I AM" (MC) in relationship with your immediate environment and the place where you are (AS).
Please note that the Ascendant, when using midpoints, is not related to your physical body and/or personality! The Sun rules your physical body when using midpoints.
Unlike the meaning of the Ascendant when using the houses, the Ascendant in a midpoint or planetary picture describes your immediate environment (i.e. the family, co-workers, everything you can encounter and that is around you, the place where you are and everything that is related to that place/environment).
The Ascendant represents the living environment and also "the others" you can meet there (other people, a partner -- in a large sense --).
This is VERY important to know. Lots of astrologers have it wrong when using midpoints because they mix up different methods and systems which often results in the wrong delineations.
To be perfectly clear, the Sun in a midpoint is about the physical body, among others, and the AS (Ascendant) is about your immediate living environment and place.
An Example from our own practice will make it very clear, though it's not always that stunning in all cases, but the example shows you loud and clear what we mean.
A client, named Nathalie, once asked us a natal analysis. In her natal chart we found the following midpoint (45° dial/list, orb 1°):
AS/MC = the #448 Asteroid Natalie
In other words, the Asteroid Natalie hit her Ascendant/Midheaven midpoint. This translates as follows:
"I am towards my environment and towards 'the other(s)' (AS/MC) Nathalie (the #448 Asteroid Natalie)"
This stunning example clearly shows how the AS/MC midpoint works out, what it represents and how it has to be interpreted!
Aside from these midpoints, you also need to take a look at the Moon's Node and the midpoints and planetary pictures in which it is involved. The Moon's Node represents bonds and connections. It shows what connects you (this can be a person or a possession or...) and is of importance in matters of love.
For example:
the Moon/Moon's Node midpoint may tell something about your bond (Moon's Node) with a woman (Moon) -- going from a sister, to the mother, to a girlfriend, etc. while the Sun/Moon's Node midpoint may represent the bond (Moon's Node) with a man (Sun) -- going from the father, a brother, a son, a male co-worker etc.
No wonder that the Venus/Moon's Node midpoint represents a "love (Venus) bond (Moon's Node)" or "love tie."