If the critical dimension is height, you have a couple options:
Hard-cropping to the exact width/height:
<?php
add_image_size( 'wide-image-icon', 200, 150, true );
?>
The hard-crop will create a thumbnail size using the exact dimensions. Be sure that all images have a minimum width/height as what is defined.
Or soft-cropping (i.e. “box-resizing”) constrained to height:
<?php
add_image_size( 'wide-image-icon', 9999, 150, false );
?>
The soft-crop with an unconstrained dimension (i.e. 9999 width) will box-resize to the exact height, while allowing the width to be, essentially, anything. Be sure that all images have a minimum height as what is defined.
Also: make sure that, if you have added these add_image_size() functions after already uploading/attaching some images, that you regenerate your thumbnails.