Did the Buddha practice Compassion in the base of Endless Spaciousness?
Yes, because that’s its limit. Beyond that base, Compassion becomes too coarse to carry on.
The Buddha was leaning mostly towards Compassion. Because in a being that is an arahant, a fully Awakened person, what happens is that the Four Noble Truths are locked in. That person only sees with the Four Noble Truths. They’re basically the blueprint of the mind of an arahant. Therefore, that mind who sees the trouble, the cause of that trouble, sees the Release of that trouble, and the Path constantly. Sees how living beings are behaving. And the kind of love or Metta that a Buddha would have, is much closer to that very strong Compassion.
That we can experience. Because of his Wisdom.