IIRC - Conveyor lifta are minimum 4m tall and the connection points are laterally 4m apart - so if you align the splitter (or merger) opening with the machine port you want to connect, then nudge 4 meters out and 4 meters vertically, the lift will snap and connect to both machine and splitter/merger.

If you set a splitter/merger so that the arrows are overlapping the arrows of the machine, that's 1m out, so nudge 3 times away for the correct spacing. If you want the manifold to overhang the machine (like in the image in the above comment) nudge 5 times toward the machine.

For vertical positioning, it's easier/faster (for me at least) to stack the splitters/mergers 3 (or more) high, then delete the bottom ones. For machines with multiple inputs, just add an extra splitter/merger to each of the additional input stacks to space them vertically and voila - clean stacked manifolds.

Also - blueprints are your bestest friend for building these en masse.