If you didn't move or resize anything the calculated zonerect is probably correct. You don't need to bother with height values unless you want to split you map into several images.
You could test the zonerect by pasting the following in the file
<YourCustomUI>\eq2map2\_User_MapStyles.xml:
<ImageStyle Name="exp05_dun_miragul_shard" displayname="Miragul's Phylactery: The Crucible" menugroup="Everfrost (Island)" zonerect="-94.45, -69.38, 137.30, 227.21">
<ImageFrame Source="images/maps/map_exp05_dun_miragul_shard.dds" SourceRect="0,0,436,506" />
</ImageStyle>
Place your dds file in the images\maps folder and rename it as in the bolded part (or change the filename in what I posted above).