There is no harm in concentrating sometimes in the heart and sometimes above the head. But concentration in either place does not mean keeping the attention fixed on a particular spot; you have to take your station of consciousness in either place and concentrate there not on the place, but on the Divine. This can be done with eyes shut or with eyes open, according as it best suits you.
The concentration in the heart is what brings about the opening of the psychic which is your principal need. If the concentration has brought about a feeling which makes you judge clearly all the other movements and see their nature, then the psychic is already in action. For this is the psychic feeling which brings with it a clear insight into the nature of all movements that come and makes it easy to reject what has to be rejected and keep the right attitude and perception. It does not matter about the image of the Mother. It is her presence whether in form or not that has to be felt always and this the psychic opening will surely bring.
The Synthetic Method of Integral Yoga, Letters on Yoga – II, CWSA, Sri Aurobindo.
Read Part 1 here: https://sriaurobindocenterla.wordpress.com/2021/01/18/the-discipline-to-be-followed-sri-aurobindo/