Help Please How to make a reliable "unlock" mechanism for vertical draggable slider?

I have a vertical draggable slider that only goes up and down two tiles total. I'm trying to create a mechanism which will prevent this slider from being pulled down until B performs an action.

Here's a front view of the setup (dots used for spacing)

···[o][o] <- the draggable switch
·······⊂|[_]
[_][_][_][_] <- 2 tile tall metal rod that's pushed by a mechanism

Right now I have it locked/jammed in the "up" position by placing a long thin tan metal rod under it. From a distance, I have B push a ball in between an automatic slider and this rod, so that the rod pushes out from under the slider and now it's "unlocked."

My issue is that about 1/3 times the ball and automatic slider jam and don't push the rod out of the way. I suspect this is because of the extra force added by the up and down slider resting on the rod that's supposed to slide out of the way.

Note in the diagram the draggable switch is resting on a sideways rounded tan block. This is to jam the draggable in the fully "up" position because apparently sliders at the very top of a vertical track sink down a few pixels, and I need mine to be flush with the top of the track. I think this jamming up is what's adding extra fricition preventing the rod pusher from working every time

 

That doesn't solve my needs because it looks like you can just pull the draggable down and it moves the balls out of the way. I want to basically force the draggable to be locked until B takes an action.

I went with my current mechanism even though it's kind of flakey and uploaded https://mekoramaforum.com/media/the-secret-of-lightning-temple.19154/. This thread is a minor spoiler for the level

 

Yes, look at my first post