Thanks PK.
I won't type out my whole response again (see above), but what you have said makes good sense. Perhaps I will be better served by changing the df-bit setting on my SRX1 rather than relying on a configuration change at the other end to make this work. However, if I can get them to update their settings as well, then perhaps that is the best result.
I had thought of the ping-of-different-sizes test but, as I don't have control over the app client - nor do I have permission to allow a test host to ping the app server - this option isn't available to me. Thus far, trying to marshall application guys to get tests like this done all at the same time has been somewhat difficult.
Thanks for your response.
Ben.