According to some embodiments, a method in a wireless network element of transmitting a transport block comprises determining a modulation coding scheme for a transmission of the transport block; determining a category type of a wireless device that will transmit or receive the transport block; determining, using the category type of the wireless device, an encoding soft buffer size (NIR) for the transport block; adjusting, using the modulation coding scheme, the encoding soft buffer size (NIR) by a factor (KH); encoding the transport block according to the determined modulation coding scheme and the adjusted encoding soft buffer size; and transmitting the transport block. In particular embodiments, the determined modulation coding scheme is 256 Quadrature Amplitude Modulation (256QAM) and the factor (KH) is 4/3.