[SR-Users] How to keep SIP messages small, possibly below fragmentation limit?

Hi

In the process of getting rid of our commercial B2Bua SBC and handling all clients directly via Kamailio...

We have come across some (unfortunately many we have in use) CPE which have an issue with fragmented packets or which simply do not allocate enough memory to parse or create messages of a certain size. Their SIP stack just crashes with errors like 'message to large for send buffer' and similar.

This affects messages with containing as little as 5 via and 4 record-route header and a couple of codec in the SDP.

Is there a recipe for trying to keep packets as small as possible?

I would like to avoid using the topos module as I issues with this module completely failing in certain situations.