You just need to look at the 400m race in athletics and see how far lane 8 begins in front of lane 1 in the staggered start.
If two runners were to start next to each other on an athletics track it would go like this...
A lap in lane 1 = 400m
A lap in lane 8 = 450m

Where it starts to get murky in horse racing is that unlike athletics the race is not usually run on an even surface.
In many cases hugging the rail is the last place you want to be while being three wide with cover can actually be an advantage on some tracks in certain circumstances.