"Better" is too subjective, what Dan said was to get a "different" scanner.
There are two types of scanning technology. Your scanner may be perfectly good, but it uses CIS technology (Contact Image Sensor). It can only focus on what is in contact with the glass. What you need to use to scan slabbed cards is a scanner that uses CCD technology (Charge Coupled Device). This type of scanner can capture some depth of field.
One is not particularly 'better' than the other. They each have tasks that they do better than the other.
Search the forums for "CCD", there has been lots of discussion about them in the past.
-Tom
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