Semiconductor-optical amplifiers (SOAs) could be used in wavelength-division multiplexing (WDM) systems with constant envelope modulation formats. However if chromatic dispersion affects their constant envelope, WDM signals can interact via the SOA carrier density fluctuations, resulting into relevant penalty. We experimentally and theoretically investigate the operating conditions for SOA-based amplification with DPSK and POLSK modulation formats and clarify the role of input power, residual dispersion and modulation format. We also determine that, for a given format, the various detection schemes can result into very different impairments. These results can be used as guidelines for the system design.