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Not sure if that gives you the idea of what i mean.
I made my own version of the Wyvera (the small one), if you look at the medium center/rear turret, that used to be 2 large ones, but the ship looks like it has always been like this, that's what i mean with welding, you make small details by hand so it looks like the pieces are built together without any "lines" that makes kit bashing apparent, however that was a bad example, as i have failed with shading on the top of those curves.
the the top piece that is the center of a Medusa, add some plating and slowly change the color from the dark blue to light blue so it looks like it belongs there. by the 2 hangars down the middle, try to get the hull appear as angled plating and have it somewhat merge with the black line's shading.
The bottom Medusa, i would just remove it or build out its top sides to merge with the ship hull.
Not sure if this comment shined some light, but in short, you need welding on those Medusa parts and around the middle.