Underfoot Trip and Equality for All

[Magabeus]

Hi there,

What do you think, do underfoot trip and equality for all stack when making a trip attempt on a large creature as a lvl4 halfling monk, underfoot adept?

Underfoot Trip:

At 1st level, an underfoot adept learns a number of maneuvers and grabs that can cause even the largest opponents to stumble and fall. He gains Improved Trip as a bonus feat, even if he does not meet the requirements.
At 4th level, and every four levels thereafter, he acts as if he is one size larger for the purposes of determining the maximum size of creatures he can trip and when determining his CMB and CMD for purposes of a trip combat maneuver. This ability replaces stunning fist.

Equality for All:

Even when facing foes much larger than yourself, you still embody the Andoran ethos of liberty. You gain a +2 trait bonus to your CMB and your CMD when facing opponents who are at least two sizes larger than you.

I am inclined to say they do not stack by RAW.
My argument: the trait bonus kicks in when calculating the CMB, then the halfling is treated as medium size, so the difference is only one size category.

[LoneKnave]

I'd say they stack. The trait makes no mention of what size you count as during a trip attempt; hence, if you are 2 size categories smaller, you get the +2 bonus, eventhough when you attempt a trip you do count larger. Counting larger does not mean your size category actually increases, or your bonus would fluctate based on wether you are tripping, grappling, etc.