Phoenix Models put lead into the fuselage at the factory. It's in the front, on the floor, just behind the firewall. They apparently did it when they discovered that their design or their choice of wood behind the CG created an airplane that was tailheavy. It is almost impossible to see. You will not notice it is there even if you look into the fuselage. It is a flat rectangle of lead.

I built mine with an OS46AX which is an average weight for the recommended engine size Phoenix suggests. Mine came out nose heavy. And I moved the battery back into the rear of the fuselage, actually behind where the trailing edge of the wing aligns. If I had known the lead was there, I would have removed it and not had to go to extra effort to build support for the battery so far aft. If they had included it in their kits for those that might need extra nose weight, I could have not used it. Had I needed nose weight, I would have placed it one the cowl side of the firewall and been able to use less than the amount needed to put it inside the fuselage.

Anyone who has not assembled their Phoenix Sukhoi has a chance to get that lead out while it's easier to do. And should, if they want the best performance out of their model and whatever components they choose. Less weight takes off easier, climbs better, and lands slower. Automatically sticking a hunk of lead into an unassembled ARF is a somewhat ignorant thing to do.