So if you tap the shifter in the manner of a normal downshift while in the biggest cog, it upshifts? And if you tap beyond that, it does nothing?
There's no "tapping". Downshifting is a very deliberate movement, more so than even on Shimano.
And no, if you try to do a "normal" downshift in the biggest cog, the shifter does NOTHING. To upshift in this situation, you, the operator, must then knowingly IGNORE the feedback the shifter is giving you (ie, no downshift "click") and then DECIDE to let go of the shifter to initiate the upshift. If you DO these to things, yes, you will upshift...(which is good, because that's how the shifter upshifts--it can't read your mind)