A flexible and efficient use of the frequency resource is a key challenge for future wireless technologies. The new requirements are not satisfied by the CP-OFDM which has motivated the research on alternative waveforms. Recently, Block-Filtered OFDM modulation scheme has been proposed. This waveform addresses most of the CP-OFDM's drawbacks at the price of a slight complexity increase of the transmitter. The scheme is based on a filter-bank, a precoding stage that ensures the Near Perfect Reconstruction property and a pre-compensation stage which avoids filtering at the receiver. In this paper, the filter specifications for BF-OFDM are derived and an optimization method based on self-interference rejection is proposed. Optimized filter shape can provide up to 70 dB of Signal-to-Interference Ratio which justifies the Near Perfect Reconstruction property with an enhanced spectral confinement and no channel performance degradation.