If you are in a poorly ventilated, crowded store and there's lots of SARS-CoV-2 circulating in the community, odds are good that you will be at a much higher exposure risk in this environment. And we already know that LTCs are tinder boxes waiting to ignite when it comes to COVID
So my take home is: yes, B.1.1.7 is more transmissible & we should be concerned about it. Yes, 6 ft/15 min is not unshakeable dogma with regards to transmission and you shouldn't treat it as absolute. Fine (but imperfect) for contact tracing, not as useful for real life.
By understanding the additive nature of risk reduction, you can reduce your own exposure risk in any situation. Dr. @syramadad and I put together this handy chart to help! Try to apply as many of these as possible rather than relying on categorical rules about time and distance.