the recommended size is the length of the python from corner to corner diagonally so they can stretch out straight but I have never seen a python stretch out like this. my 7YO Childrens is comfortable in a custom built 70x60x60
It's a bit weird when some random idea gets touted as "the" recommendation.
Most people don't follow this recommendation. Snakes don't need to fully stretch out. Even with all the space they could ever want they very rarely ever 'want' to stretch out dead straight. I guarantee you will never, ever, see a snake stretch out dead straight corner to corner as you describe.
Snakes generally do best in something around half the length of their own bodies. There is no fixed rule or universal recommendation. If the enclosure is well designed you can usually get away with a larger enclosure if you want to, but even then it's usually just wasted space and the snake will only use the area it likes most, and to make a snake use the whole thing you generally need to force it to, such as by using complex heating systems which make different areas comfortable and inhospitable at various times, forcing the snake into whichever area is habitable at various times of the day. Some people argue this is good for the snake, but even if that's true, it's very difficult to set up and extremely dangerous since it will probably malfunction at some stage even if you initially get it right, which most people would have no hope of.
Being able to 'stretch out' has zero to do with keeping a snake happy in the real world.
As for the original question, the 90 x 45 x 45 is more likely to keep the snake happy, all else being equal. The vast majority of captive adult Antaresia are in enclosures smaller than that.