Basic 4th street situation in Stud 8.

[dibbs]

I'm still unsure of this scenario, pretty common though.

You start with a 3 card low, a few players see fourth. One player catches what appears to be an improved high hand (not a paired door card though), and bets, and it gets folded to you.

How big does the pot have to be and how versatile does your low have to be (A36 with live aces, ,234, 345, 456, A27, 2s3s7 etc.) to call headsup? I'm playing with numbers from various situations but thought I'd ask here as well.