Speaking of attacking Kushan Central Asia, as well as the part of South Asia that doesn't rely on the sea, the Han Dynasty has no problem maintaining supply lines. But once past the Central Asia part and into true South Asia, the largest distance of most territories from the coastline is just over a thousand miles.
That means if you strike from Aksai Chin through Central Asia, with the Han Dynasty's strong military power, there's basically no problem. But not only must Chen Xi still build a road, even coming out of Aksai Chin and striking near South Asia, you will still be restrained by the Kushan Navy.
A distance just over a thousand miles with the current godlike marching speed means you can be ambushed and surrounded effortlessly, as long as Kushan can think straight. At this point, they can easily cut off the Han Dynasty's supply line, and no matter how extraordinary their military might, they can't continue advancing.
