When placing your connections, keep in mind that the flow of current through the material will dictate how the fabric heats up. The heat will be concentrated at the sources of current and radiate along its path and outward. You can see this in the examples below, where I experimented with connection placement.
For these tests, I used a 5" square of conductive heater fabric and connected a 12V power supply using alligator clips. I placed a piece of cotton broadcloth painted with thermo-reactive fabric paint on top of the heater fabric. The blue areas in each image show the heated areas.
1. The distance between your power and ground wires matters - if they are too close you will get a very hot spot that could smoke/burn, and if they are too far apart the heat will concentrate around each connection point.
2. If you decide to connect power and ground in multiple places along the piece of fabric, the distance between each set of power and ground connections must be consistent. If one set of connections is closer together, the heat will concentrate between them.