I like your subtle omission of parens from h$a, versus h($b). But to sort correctly, I tweaked slightly to use the OP's 10,20,30 values.

perl -e 'sub h{pop=~/(...)(.)/&&$1*2**{K,10,M,20,G,30}->{$2}}print sor
+t{h($b)<=>h$a}`du -h`'
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