water level in the sump or tank will not affect anything on the weipro PS
if it is put outside when put in the sump .. water level should be higher then sump water level . water level in the PS is determined by the water output (faster output, = lower water level , slower = higher water level). adjusting would be done at the valve .
if the outlet of the PS is already maximum and your PS still overflows,then check if there is any blockage to the output hole or did u modify the output pipe , the output pipe should not be modified longer or shorter coz this will effect the water output rate (example : head loss on a return pump the further and higher pipe line will effect flow rate)
lastly , if everything is normal no blockage or modify then the pump is might be overated meaning the water input is too fast than the PS can output .