Don - the tandem match diodes on Aliexpress units sometimes are not the correct BAT41 or 1N5711 diodes, causing incorrect readings.
You could try changing cell 31 values until your tuner agrees with your wattmeter. Normally, this cell is set for 10 when there are 10 turns on the BN43-202. The manual is on David's github site
Be sure to keep a copy of the current firmware as written to the 16F1938 controller...
GL de Russ, va3rr
va3rr