The spar piece you see is just a wooden form used for mockup...not a real spar. I cut .150 thick shims to simulate the 10-bid layup that connects the spar to the longerons, then made the mounts to fit. When I make the real spar, I'll make the wood core (I'll use oak) hard points larger as needed to accommodate the mounts.
The top mounts extend farther FWD up the longerons than the lowers do, and even though they don't occupy quite as much surface area on the spar as the lowers do, they're still alot stouter, have more bearing surface and distribute the load better than the plans aluminum angles. Certainly alot stronger than what they are hooked into. I'll end up with more than 10-bid for the connection layup, and I'll probably run the first few layers further FWD on the longeron and inside skin to help distribute the load into the airframe.