As Sri Aurobindo has explained in a number of letters (and so has the Mother), doing sadhana has to do with the sincerity of one’s aspiration, faith and surrender rather than by the place where one lives in. Also, we need to keep in mind that their letters were written, obviously, when at least one of them were present in the Ashram in the physical body, which changes the meaning of a question to physical proximity to the Guru, a totally different aspect.
This is not to say that certain places (the Ashram being the foremost) are not helpful to the sadhana. Without a doubt the Ashram is such a concentrated space that helps the sadhaka in many ways. But also due to the intensity of the Yoga Force working here it also makes it difficult to live under the intense pressure of change that one experiences here. This pressure often brings out hidden resistances that can be too demanding upon the sadhak to deal with unless he is well rooted in equanimity and surrender and keeps his faith intact through the process. At the same time there is often a flagging of the aspiration here just as thirst diminishes when one is surrounded by water all around. Besides the Ashram as a collectivity allows a certain degree of freedom (needed for any authentic growth) but not all are ready to handle this inner freedom.
Outside the Ashram one lives by social pressures that keep one tied within a largely fixed form of life that often stifles the urge to grow. The demands for the maintenance of family life and its outer apparatus also drain an enormous amount of energy. These are some of the different challenges one meets when one lives here or outside. Yet if we have the right attitude each such challenge becomes a unique opportunity for growth along certain lines of our nature. Ultimately whether one is called upon to do the sadhana in Pondicherry or outside is a question of the soul’s choice and its unique destiny. But the idea that sadhana can be done only in Pondicherry is obviously incorrect.
Here are words from a letter by Sri Aurobindo to a disciple living outside the Ashram:
“The Mother is always with you. Put your faith in her, remain quiet within and do with that quietude what has to be done. You will become more and more aware of her constant Presence, will feel her action behind yours and the burden of your work will no longer be heavy on you.”