First of all, WES requires HSC documents from all Pakistani candidates, no matter what degree they require to asses.
For example in my case, I did my masters degree form Germany, Bachelors and HSC from Pakistan.
WES didn't provide me ECA until they received my HSC transcript and certificate from Board of intermediate education Karachi.
So, if you have done your HSC/I.Com etc from Pakistan, you must submit your HSC transcript and certificate to WES, otherwise they will not provide you ECA. Moreover, as Bachelors degree comes between HSC and Masters, you must also provide your Bachelors degree to WES.
Also, It is highly recommended that you should get ECA for all your degrees (From HSC to Masters) and not just the last degree (which is Masters in your case).
Hope this helps.