I had this same question. We set up a bunch of banners as an XT; the activity conversion metric is CTA clicks. Every visitor who loads one of the pages sees a banner, and some clicked a CTA. So the A4T report shows visitors, conversions, and a conversion %. You can compare visitors in the experience to overall visitors, but there's no control or A/B, so no lift. And there's no way to segment the experience visitors who saw the banner AND clicked a CTA from those who just saw the banner.
To address that last issue, we added Custom Link tracking to the CTA, like so:
$(".banner_button").click(function () {
window.s.tl(this, "o", bannerName);})
So now in AA Workspace, we can see clicks by banner name, and segment users by those who clicked on all banners or those with matching names. We could narrow that down to individual banner names, but it's a bit tedious.
What we now decided to do is add tracking tags to the target URLs of the CTA buttons. That way, the users who clicked on a button or group of buttons will fall into a campaign visitor segment. You can use the internal campaign variable designated for this purpose (icid=) but we just use our regular campaign tag, where all the metadata lives in SFDC and is ported into AA as Campaign classifications, and we set the vendor field to Internal.