457b plan as an emergency fund

I already max out my 401k, but my employer offers a 457b plan as well. Already have an emergency fund (about 6 month worth at current spending level, probably 12 months living expenses on SHTF spending levels). You can cash out a 457b plan without the 10% hit, if you are no longer employed or have a major emergency (illness, disability).

I was thinking of decreasing the amount of $ in emergency fund to about a 3 month level and funding the 457b plan to at least a 9 month level over the next couple of years. Am I overlooking anything or is this a good idea?