Try this:
Stand with both feet flat on the floor, seperated front to back maybe about 75 cm and body exactly in between, legs straight.
Now articulate your feet, so that your front toe is raised and your back heel is raised.
Where did your body go?
If you said it's still in the middle, take a look at your back knee. It's not straight any more, is it.
Start over from flat feet and then articulate them again, this time keeping both knees straight.
Where did your body go?
That's right, it's now substantially closer to the front foot than the back one.
The triangle is not isosceles - the back leg with it's raised ankle is effectively longer than the front leg with it's low ankle - or it would be, if your remembed not to bend that back knee.