How to filter the tasks using custom field value - ProjectServer Rest OData API 2013

Question

I've been trying to filter the Task collection using custom field called "TaskType" (I've created this one). This custom field has an associated lookup table. So if i query the OData :

https://myserver/PWA/_api/ProjectServer/Projects('0647003e-dce3-e211-9477-080027efb62d')/IncludeCustomFields/Tasks

I get the following custom field data:

 "Custom_x005f_fe7ff100cee3e2119477080027efb62d":{
   "results":[
     "Entry_960a8ffef3334cc2bfee14a27cf95dbb"
   ]
}

since this is an array I can't filter using this field. I can extract names of the assigned custom fields, but not the value. so the following query

https://PWA/_api/ProjectServer/Projects('0647003e-dce3-e211-9477-080027efb62d')/IncludeCustomFields/Tasks?$select=CustomFields/Name,CustomFields/LookupEntries/Value&$expand=CustomFields,CustomFields/LookupEntries

would return something like this

{
   "CustomFields":{
      "results":[
         {
            "LookupEntries":{
               "results":[
                  {
                     "Value":"Normal"
                  },
                  {
                     "Value":"Auto"
                  },
                  {
                     "Value":"Manual"
                  }
               ]
            },
            "Name":"Task Type"
         }
      ]
   }
}

Is there any association between Task and its Custom Field Value so that could be used to filter the results?

Using the ProjectData API is not something I want to go into.