tshark crashing because of temp pcap files in /tmp

I am trying to run tshark for an extended period of time to reassemble NFS requests that I capture using tcpdump (with pf_ring). I am streaming the pcap to standard out from tcpdump (using -w -) and into tshark (using -i -). It seems that tshark calls dumpcap to do the packet capture (even from stdin) and then dumpcap writes the packets to the /tmp directory and then tshark reads from there. The reading and writing to disk was a bottleneck for me so I specified a new location using the TMPDIR environment variable and set it to a tmpfs mount. This was successful in speeding up the tshark processing but once the tmpfs mount fills up, tshark crashes. First, I would like to confirm that this is the correct behavior. If so, I have two questions:

1. Can we remove dumpcap from the equation if we are just reading from stdin (so that it is similar to reading from a file)?
2. Is there a way to tell tshark to roll the temp files (similarly to how it will roll the raw packet captures if using the -w argument) so that it just overwrites old files rather than filling up the directory until it gets an Out of Memory exception?

Thank you.