Elasticsearch filter range on nested objects

I have an object PurchaseOrder that has a List<VendorStatus> VendorStatuses, VendorStatus has an EstimatedShipDate column. I need to filter a purchase order by the latest EstimatedShipDate. How can I do this?

I've tried:

Filter<PurchaseOrder>.Range(r => r
    .OnField(x => x.VendorStatuses.OrderByDescending(v => v.StatusUpdateDate).First().EstimatedShipDate)
    .GreaterOrEquals(fromDate)
    .LowerOrEquals(toDate));

and

var f = Filter<PurchaseOrder>.Range(r => r
    .OnField("VendorStatuses.EstimatedShipDate")
    .GreaterOrEquals(fromDate)
    .LowerOrEquals(toDate));

and

var newFilter = Filter<PurchaseOrder>.Nested(nfd => nfd.Path(x => x.VendorStatuses.First().EstimatedShipDate))
    .Filter(f2 => f2.Range(x => x.OnField(f => f.VendorStatuses.First().EstimatedShipDate)
    .GreaterOrEquals(fromDate)
    .LowerOrEquals(toDate))));

But none of these worked. How can I do this?

I'm not even able to get the date range working when running against elastic directly. The following query returns no results even though when using the head plugin i can see them listed under "po"

{
    "query": {
        "range": {
            "po.vendorStatuses.estimatedShipDate": {
                "gte": "2016-10-01",
                "lte": "2016-11-01",
            }
        }
    }
}

We're using Nest version 1.7.2 in our project with elastic 1.4.5.

Here's some more info on our types:

//that builds our search query, contains many methods to build up the FilterContainer
public class PurchaseOrderSearchQueryBuilder 
{
    protected FilterContainer Filter { get; set; }

    public PurchaseOrderSearchQueryBuilder WithExpectedShipDate(DateTime fromDate, DateTime toDate)
    {
        var newFilter = Filter<PurchaseOrder>. 
        //method i need to implment

        Filter &= newFilter;

        return this;
    }
}

//example working filter method
public PurchaseOrderSearchQueryBuilder WithCustomerId(long customerId)
{
    if (customerId > 0)
        Filter &= Filter && Filter<PurchaseOrder>.Term(p => p.CustomerId, customerId);
    return this;
}

public class PurchaseOrder 
{
    ...
    public long CustomerId { get; set; }
    public List<PoVendorStatus> VendorStatuses { get; set; }
}

public class PoVendorStatus
{
    public long Id { get; set; } 
    ...
    public DateTime? EstimatedShipDate { get; set; }
    public DateTime StatusUpdateDate { get; set; }
}