Taijiquan is not simply relaxing, sinking and being grounded. It is about developing; the right structure; the right sequence of movements to connect the structure; the right timing of the movements; and the mind awareness (Yi) to travel through the movements.
A structure without the sequence of movements is like an electrical cable without the copper wire inside the plastic tube. Without the mind awareness (Yi) even the correct structure with the right sequence and timing of the movements, is like the wire not having a current passing through it.
Connecting the Base and Arms
Often the movements of the base (feet, legs & hips) and the arms are co-ordinated but unconnected, and therefore incorrectly act independent of each other. The connection between the base and arms is in the body's torso and needs to be cultivated using the mind awareness (Yi) to create a melting sensation through the body as it leads the force from the feet to the finger-tips.
When initially practised it is difficult to recognise anything happening but after a few years of training it is possible to feel even very small muscles in the body change as the mind directs. Eventually the base movements will actually produce the movement in the body which in turn will produce the movement in the arms, both during sinking and issuing.
It is easier to first cultivate the body connecting the base and arms in static foot positions and repetitive movements such as in Master Huang's relaxing exercises before involving the stepping and changing postures of the Form. Later work it with the addition of an external force in the controlled environment of fixed pushing-hand routines, before attempting it in the free pushing, where the external force direction and speed is not restricted.
Once the whole body is continuously connected, and the timing becomes almost natural, neutralising would involve allowing an incoming force to pass through you into the ground where it would be combined with the energy of the earth and rebounded in greater magnitude back to the source of the incoming force. This "interception" does not require you to initiate any issuing as your body will have become a medium for the forces to pass through unimpeded.