wrote: Setting ignore mtu mismatch for OSPF is generally a good idea when doing interop.
No, setting ignore MTU mismatch is not a good idea. There is a reason OSPF refuses to bring up an adjacency by default if there is an MTU mismatch. If you mask this by ignoring the mismatch, you could end up in a situation where DBDs can not be successfully exchanged if they are too big. This is a difficult problem to troubleshoot as the adjacency will appear to be functional, but your LSDBs will be inconsistent.
The correct solution is to make the MTUs at both ends of the tunnel match. This can be set manually on the SRX side; you'll have to check Mikrotic documentation to see if this can be done on the other end.