RocketcarX
95% of my weight is fuel
O2 extensions are normally for the rear but some like myself have used them up front. The sensors are the same they just have different connectors. If you cut the tabs on the front sensors you can plug them into the extensions. That is why you have two different colors on the connections. As long as you have them going to the right spots it really doesn't matter.
If you have long tubes you will need them for the front sensors. Most people lose the rears in the tune at that point.