No, your reasoning is incorrect. Food safety rules are dumbed down because they have to be taken literally without any reasoning.
if the temperature is very high all the time during that time, I think the maximum time is shorter.
The maximum holding time isn’t shorter for higher temperatures. It is the time at which food is legally safe, and it is defined to be the same for all temperatures in the 4 to 60 Celsius range, for all foods. This is different from the time the bacteria load actually increases to different levels – the real time cannot be really predicted, so the food safety rule assumes the worst case plus a safety margin.
Package isolation, actual temperature difference, actual initial bacterial load and so on are variables which you cannot measure at home, and whose effect you cannot calculate without using a model sophisticated enough to do a weather prediction (and we all know how good these are). So, they are not considered when calculating the legally safe time.
The range of 4 to 60 Celsius was chosen because it is the range at which foodborne pathogens multiply. Below 4 Celsius, Salmonela stops multiplying (but doesn’t die, neither do other bacteria). Above 60, a few bacteria will survive, but practically none will multiply. The 40 Celsius limit is very low, even humans can survive it. It is a very comfortable temperature for most foodborne bacteria, whose optimal life condition is the gut of a human suffering from a fever.