Awesome O_O"Close but a bit incorrect. You create a portal directly in front of you, that stays dormant, so to speak. After you use a jutsu, a small amount of Keigoku is released in the process of the attack. Due to your rank, being a Black Knight, your Keigoku can go through trees and stuff, so say you shoot that fireball and someone tries to block with a wave of water. It'll put that fire out but the keigoku will still travel the range of the jutsu you used, meaning the keigoku will still go through the water and possibly effect them, making them have to use likely two jutsus to defend against only one, or dodge the keigoku even after defending against the water.
Try again.
As for the question, the range of the jutsu used stays the same. The Keigoku travels as far as the jutsu used can travel.
I start out by focusing my chakra out in front of me and readying a portal that stays dormant, hidden to the naked eyes. I then proceed to wave a few hand seals as I exhale a fireball from my mouth, heading towards that magical clone you've made. As the fireball is leaving my short range, I focus my keigoku and open up the portal, allowing a portion of the keigoku to slip out and mix with the fire, allowing it to become a combination of sorts.