I don't know exactly but, as far as I'm aware, the CDC hasn't issued any updated guidance about high risk situations with the emergence of Delta.
The higher level of transmissibility could mean that it is more likely to transmit under the same high risk conditions but doesn't bring new situations into the fold of being high risk. I guess what I'm trying to say is that, with no information to the contrary, Delta doesn't infect people 15 feet away, it is just more likely to infect somebody 3 feet away. Perhaps it does it in less time due to the higher viral load but if it is five minutes instead of 15 minutes that is high risk, you still don't spend five minutes close to the same stranger at a grocery store.