this was born as quick hack, as always..
I think is simpler to remember that you need to pass a width X height x infix then others things. You can easyly modify the code to change both dimension if it is what you want (from module documentation):

resize($width, $height, $constraint);
Returns a GD::Image object for the new, resized image. Original image 
+is not modified. This lets you create multiple thumbnails of an image
+ using the same Image::Resize object.

First two arguments are required, which define new image dimensions. B
+y default resize() retains image proportions while resizing. This is 
+always what you expect to happen. In case you don't care about retain
+ing image proportions, pass 0 as the third argument to resize().
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L*