I get similar results with the zooms and my 1.4x tamron. But like you found with the tamron 90mm... the tc's do work better with the primes.
The atmospheric conditions and phase of the moon really make a huge difference. The night after I got the shot below,
I tried again and could not even get close to that detail, because of conditions in the upper atmosphere
Here is a moonshot with an old 400mm vivitar F5.6 and the tamron 1.4 tc
this is probably the most detail I got on a moonshot.. I gave up trying not long after this...
PS full moons are the toughest to get detail out of... the most detail tends to be near the shadows,
and there are not many shadows on the full moon
