Issue with acceleration in PX4

when using offboard mode with “make px4_sitl_sih sihsim_quadx” and using the set acceleration ned, if I set the acceleration to 20 north and like -1 or -2 down, the velocity northwards of the drone caps at 12m/s and if I set the acceleration to 1 north the velocity of the drone caps at just above 1 without any changes to the drone parameters. Does anyone know what might be causing this?

Thanks for your help.