Bolt distance shall be 48.5/2 (half of post diameter) + 1.5x16mm (min. requirement for M16) + 3.0mm (welding thickness) = 51.25mm say 50mm.
Center line of bolt to edge of plate shall be 1.5D = 1.5x16=24mm say 25 mm.
Thus base plate at post location shall be 25+50+50+25 = 150mm. In the drawing given 120mm, it is too small, washer might be over welding joint which is not good.