What's the best way to accurately tell if a specific part is touching a button?

So I'm working on a puzzle game that uses Portal-style "put the cube on the button" mechanics.

For the buttons, I'm using this script:

script.Parent.Touched:connect(function(activator)
    if activator.Name == "Activator" then
        script.Parent.BrickColor = BrickColor.new("Sea green")
        script.Parent.SurfaceLight.Color = Color3.new(0,170/255,127/255)
        script.Parent.Parent.Particles.ParticleEmitter.Color = ColorSequence.new(Color3.new(0,170/255,127/255),Color3.new(0,170/255,127/255))   
    end
end)

script.Parent.TouchEnded:connect(function()
    local shouldBeActive = getTouchingParts()
    if shouldBeActive == false then
        script.Parent.BrickColor = BrickColor.new("Plum")
        script.Parent.SurfaceLight.Color = Color3.new(1,0,1)
        script.Parent.Parent.Particles.ParticleEmitter.Color = ColorSequence.new(Color3.new(1,0,1),Color3.new(1,0,1))
    end
end)

function getTouchingParts()
    local num = 0
    for i,v in pairs(script.Parent:GetTouchingParts()) do
        if v.Name == "Activator" then
            num = num + 1
        end
    end
    if num == 0 then
        return false
    else
        return true
    end
end

It works, but it's buggy. My main problem is that it occasionally fails to register the touch happening or ending.

I dunno what to do; making it a while loop simply returns a script timeout.