So here is how i see it. He does not have the volume control - air release. I dont use them anymore, and try to design the "air inlet loop" to let in just a small gulp of air each cycle. If its too much you simply get a burp in the upstairs toilet every now and then. It worked before for him, so his air intake system probably roughly matched the air absorbtion of the water in his tank. So the question we must ask is what did he do besides fixing the bad check valve with the schrader valve on the WELL side? He put in a normal check valve and tee'd in a schrader valve on the pressure - house - side of the check valve.
I calculate a guess that by moving his schrader valve to the tank side of the check valve, he created a venturi or "micronizer" type valve that simply sucks air in continually on each run cycle.... causing air overload. I think that valveman might agree that he must replace the schrader valve on [or to] the well side of the check valve before seeking leaks in the drop pipe.
So to answer the question "did I do something wrong here?" it is a big yes. Its like that little thing that that guy did at Chernobyl that "seemed" right, but was just a bit wrong. Put it back like it was [you can buy the check valve tapped for the schrader or tee it in on the well side of the check valve] THEN think about the drop pipe if you get too much air.
Wanna do a quick test? put a big wad of chewing gum on that schrader valve, get your tank empty of air, and run some cycles. I think your tank will stay waterlogged, and the pump will short cycle.
When the schrader valve is on the well side of the check valve it only operates [opens] when the pump is off and the drain down fitting or valve [hidden to him] is open. If the schrader valve is on the tank side of the check valve it may or will open under suction, which is what it "see's" when the pump runs. If he could control that suction, he could actually leave it in its location [micronizer type valve] and adjust the air intake to not overload the tank. Intriguing bit of plumbing error!