I know they did it in the part right before you get to wheatly's chamber, with the excursion funnel.

To attempt to clerify further.

I have an angled spray, and I need to cover a wall. The only portable place is on the floor, and the gel effectively sprays onto the wall up to the top of the spray, and random splatters cover down to the floor (mostly). I still need it to go a little higher, and i'd like there to be a clean strip from top to bottom instead of the messiness that i get with this result.

goodwinter wrote:
I've not actually tried this but I would imagine all the min/max values attribute to the randomness of the gel, which would consequently paint your surface. Varying parameters like min/max blob speed, spread radius and spread angle might help you achieve the whole area being painted as opposed to an accurate spot.

accuracy isn't quite the issue here, it's more of no matter where you place the portal, the paint can't reach as high as it needs to. Changing the speed messes up painting the other required parts of the chamber.