Some proliferation tricks. If you have more ideas, but don't know how to make it, please reach out to me in the discord and I can add it to this BP.

The proliferator's hitbox is a strange thing.  For the belt that gets sprayed: it is possible to 'clip into' the proliferator with blueprint slide.  This only works in one direction (going in) and not in the other (going out). Thus, you can make T-junctions, or let the belt clip in from below (Part 1 of the blueprint). All with the blueprint slide technique.

The belt that carries the spray will fill the sprayer if it is close enough, as the examples in part 2 of the blueprint show, you don't have to go exactly through with the belt. half a belt dot far away is close enough. You can also clip in from the back, with blueprint slide, to make a T-junction.

In the third part of the blueprint. There are 2 simple self-sprayers where I have only used normally pasted belts. And a third that is fully inline using the clipping methods described above plus some belt dot bending.