BizTalk latency issue when consuming web service

I’m having BizTalk latency issue when consuming a web service.
The scenario is as follows:

1. Application A sends request messages to BizTalk Server 1-way HTTP receive port locations.
2. BizTalk Server routes the request messages to a 2-way (solicit-response) HTTP Send Port.
3. The 2-way HTTP Send Port sends the request messages to another
Application B.
4. Application B processes the request and returns response messages
synchronously to BizTalk Server.
5. BizTalk Server routes the response messages to a 1-way HTTP Send Port.
6. The 1-way HTTP Send Port sends the response messages back to the
requesting application A.

(Same scenario as described here:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/BTS_2004WP/html/87f447a2-09ce-4a30-9f94-584684310051.asp)

The latency issue is in step 3-4, it takes ~2 seconds to receive the
response.

If I skip BizTalk and requests Application B immediatly from a i.e. a
windows application, there is no delay (30 ms).
It does not make any difference if I send 100 requests in parallell to
BizTalk, every request-respond to Application B takes ~1,5-2 seconds
seriellt -> ~200 sec.

I have tried all the optimization tips given in the Microsoft-article
(BizTalk Server 2004: Performance Tuning for Low Latency Messaging, link
above), including setting the
HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Services\\BTSSvc.3.0\\ HTTPReceive
– HTTPBatchSize = 1 in order to force BTS to do all request immediatly.

Have you experienced the same issue, having any tips, a name or anything that might help or put me in the right direction would be very appreciated!