The issue is that A/B testing only looks at outcomes, not reasons. There is a possibility that having the sign-up button above the fold wasn't the contributing factor here, or that it was only a contributing factor. Having to scroll through an estimate may lead a potential customer to believe that pricing is too complex or, worse, that the vendor is trying to hide something. Perhaps there are other reasons. The problem is that A/B testing will only tell you the what and not the why.
If it was your average modern startup page where you have to scroll down 3 screens to see anything besides generic marketing drivel and licensed stock photos of smiling corporate drones, of course reducing whitespace so people can see what the product is about will increase signups.
