here's a pretty decent article on heat training and its benefits:
https://www.podiumrunner.com/heat-training-benefits_161570
and another article where heat training is touched upon by pete magill:
https://www.podiumrunner.com/running-and-beer-heat-altitude-and-muscle-fuel_177716
my personal opinion: everyone's different, but in a 1 mile race, heat shouldn't be a significant factor for a well-prepared athlete (and there is some ambiguity in this term). for me, it's insignificant in races up to 5k, but i have done a fair amount of heat-running in my career here in southern california, so that's probably given me a mental and physical edge, enough so that i always enjoyed racing in the heat because even if it did affect me, i figured it'd affect most other runners more. whether it was true or not probably mattered less than me believing it was true, but after reading the above articles recently, it appears i had a physical advantage that i was unaware of...
hope this helps,
cush