Due to the way Sony embeds its JPEG thumbnails within the ARW files; there's not a lot we can do to fix this. However, there are 2 solutions that you use to fix this!
Solution 1 - Shoot RAW + JPEG
If you shoot RAW + JPEG with Sony; you can go into Aftershoot's settings and make sure that you have instructed Aftershoot to read the accompanying JPEGs for your RAW images.
Doing so will instruct Aftershoot to render the accompanying jpeg files instead of relying on the embedded thumbnail which has a lower resolution
Solution 2 - Use Lightroom to convert ARW to DNG
An alternate solution might be to convert your ARW files to digital negatives using Lightroom.
Once done, you can import the DNGs into Aftershoot and it will cull and show you the full resolution thumbnails for your images