Interesting question.
When you use the term "balance", it sounds like you would like to achieve a perfect square figure, but what is needed here are easy aspects to the planets in the T-square to help soften it, and diffuse it, like IleneK wrote.
Closing the T-square would not "balance" it, it would end up blocking the energy, it would have no outlet and it would continue to play off itself.
If the focal point sits on your ascendent it would effect your ascendent, and probably be effected by it. It would work both ways.
Can we use a concrete example?
Ascendent in Leo. Descendent in Aquarius.
T-square mars in Leo, squaring an opposition of moon in taurus and Saturn in scorpio.
So we have mars sitting on your ascendent, stimulating it and simultaneously interacting with moon and Saturn. You would become irritated, you would find your personal expression hampered by Saturn squaring, and at the same time being touched internally by the moon square.
Your reaction would also trigger the conflicting energies of the T-square in the other person, setting off their negative reaction, their contact with your personality would agitate them.
However, would it be pulling energy from your descendent, or maybe giving energy to your descendent?
We would have mars opposing the descendent, with moon and Saturn squaring it.
So these energies would materialise, they would play out in matters of the descendent. The relationship would be in turn overly emotional (moon square), cold (Saturn square), irritable (mars opposition).
But would the descendent on the other hand "complete" the planets? By concentrating on the relationship, will the T-square person find a resolution of their conflictual energy?
They might use the relationship as a way of emptying the T-square, of releasing the negative energy by focusing on the descendent. Which is not really the same thing as completing the T-square.
And I'm not sure why, but I suspect the mars/descendent opposition would play out less strongly than the Saturn/moon opposition to the descendent.
Not sure if this is a help, I'm looking forward to hearing feedback on this. Thanks for asking.