First photo Scott 203 (London printing on the left) and Scott 222 (First Peking printing on the right)
London printing shows weak or fine shading lines under top panel, right hand pennant long, clear diagonal lines in the sails and the wave above the H does not touch the junk. In the Peking printing the shading lines under the top panel are heavier, the right hand pennant is shorter, the diagonal lines are not as distinct and the wave touches the junk

Second photo Scott 207 (London) on left and Scott 226 (Peking) on right

Not all diagnostic characters are visible on all stamps, and I find the diagonal shading lines to be ambiguous at times, as I find them quite apparent on my Scott 226