SINR versus transmission rate
If your power is fixed, then as you increase your bit rate, the energy per bit interval is decreased at the same rate. You can think of this as integrating the power over the length of the bit. If you integrate over less time, your energy for that bit will also be less. Specifically, if you double your rate, you cut your energy per bit in half. This is why the SINR is inversely proportional to the rate.