How can I refactor this LINQ to be more performant?

Question

I have a console app that processes orders generated since 18:30 on the previous day. The method returns an array of order numbers.

The first operation is to retrieve a list of orders from a table called Docstore (which contains orders that have been printed, which are the only orders that are needed) into an array:

string[] orders;
using (var db = new TCRContext())
{
    var query = from docs in db.Docstore
                where docs.DateCreated >= fromDate && docs.DocumentType == "InvoiceCredit"
                select docs.PrimaryKey.Trim();
    orders = query.Distinct().ToArray();
}

Typically there may be at most 40 such orders. There are a couple of further considerations. First, there's a database VIEW called MatchingCustomerOrders which JOINs Orders (from the actual Order table, not the Docstore table) onto another table CPCustomers which contains a subset of all the company's Customers who participate in this particular operation (about 90 out of 2,370).

CREATE OR ALTER VIEW [dbo].[MatchingCustomerOrders]
AS
SELECT 
    Orders.order_no,
    Orders.invoice_date
FROM     
    Orders INNER JOIN
    dbo.CPCustomer ON Orders.customer = dbo.CPCustomer.Customer
WHERE  
    (dbo.CPCustomer.IsDeleted = 0)
GO

So we only need orders that match these customers. And we want to restrict them to those which match the invoice date parameters (i.e. from 18:30 the previous day to now) and also we don't want to process orders that have already been processed (hence the ProcessedInvoices part)

var query = from matches in db.MatchingCustomerOrders
            where orders.Contains(matches.order_no.Trim())  && 
            !(from processed in db.ProcessedInvoices select processed.order_no.Trim()).Contains(matches.order_no.Trim()) &&
            matches.invoice_date >= fromDate.Date && matches.invoice_date <= toDate
            select matches.order_no;
orders = query.Distinct().ToArray();

This is not particularly performant because the VIEW MatchingCustomerOrders has 90,000+ rows, and my suspicion is that LINQ is operating over the whole set. I've been banging my head trying to refactor this but none of my solutions seems to work.