Problem with Atlas Y turnout

[RobertInOntario]

I'm working on a small 1x4' shelf switching layout. The layout is coming along well & I'm pleased with it. All of its turnouts are either made by Peco or Hornby*, except one, which is a Y turnout made by Atlas. I'm having problems with the latter -- all of my newer locos pass through this turnout OK, but I'm having trouble with my older ones. The older ones either derail or stall as soon as they touch the guard rail of this Atlas Y turnout. As soon as they hit the guard rail, you can see their wheels rise up as if they're trying to drive over the guard rail.

My theory is that, b/c the wheels/flanges of these older locos are coarser, they are too thick to pass between the rail and the guard rail. As a result, the wheels either get stuck or get pushed up over the guard rail. To solve this, should I try to slightly widen the space between the rail & the guard rail, or should I lightly sand down this plastic guard rail? Just want to check first before I possibly wreck this turnout with my surgery. Thanks in advance.

Rob

*(FYI, this is a British layout, which is why I've ended up using some Hornby track. Hornby & Peco track and turnouts are excellent, but I've had problems with Atlas turnouts several years ago. In recent years, they've seemed to be better, so I thought I'd be OK to use one now.)