If you're looking for an actual distance, I think it's generally agreed that 1 to 2 metres between the controller and first pixel should be ok. Shorter is better. As usual YMMV and all that.
Ed dropped into chat tonight (here) while on his way to church. The update was: "multicast fixed and uploaded. round-robin delay fixed. flickering last pixel (sometimes) finally found and fixed. just about done with effects. should finish today. includes RGB-xxx, nulls, repeats, reverse."