UNION ALL within a view

I have a client who has viewes that contain UNION ALL command for number of very large tables. The logic is to apply a WHERE condition to that view to get the data. Even having indexes on those tables SQL Server applies a WHERE condition to each SELECT statement within a view that may lead to performance proble. To demonstate it please considetr AdwentureWork data and two tables Sales.SalerDetails and SalesOrderHeader

CREATE VIEW v1
AS
SELECT S.SalesOrderID
FROM
Sales.SalesOrderDetail S
UNION ALL
SELECT S.SalesOrderID
,S.CreditCardID FROM
Sales.SalesOrderHeader S

SET STATISTICS IO ON
SELECT TOP 100 * FROM v1 WHERE SalesOrderDetailID >40000 AND SalesOrderDetailID<45000

Table 'SalesOrderDetail'. Scan count 3, logical reads 1359, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'SalesOrderHeader'. Scan count 1, logical reads 34, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

You can see that SQL Server 'touched' those tables by using Clustered Index Scan on
Sales.SalerDetails and Clustered Index Seek on Sales.SalesOrderHeader. Indeed I realy simplified the logic as in reality it has horrible performance. How to improve?

I create a Multi-Statement Table-Valued UDF that accepts a parameter
CTREATE FUNCTION dbo.udf1
(
@SalesOrderID INT
)
RETURNS @t TABLE (c1 INT,c2 INT)
AS
BEGIN
INSERT INTO @t
SELECT S.SalesOrderID
FROM
Sales.SalesOrderDetail S
WHERE SalesOrderID > @SalesOrderID AND SalesOrderID<@SalesOrderID+5000
UNION ALL
SELECT S.SalesOrderID
FROM
Sales.SalesOrderHeader S
WHERE SalesOrderID > @SalesOrderID AND SalesOrderID<@SalesOrderID+5000
RETURN
END
Table '#74AE54BC'. Scan count 1, logical reads 12, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

See , I applied a WHERE condition within an UDF for every statement as UDF must get parameters.This is another argument to use Table-Valued UDF ...