You won't find many recreational bootboards that aren't 4 degrees.

As Matt mentions, there is no standardized way of measuring forward lean (kind of like flex index and what angle to measure forefoot width at), and the surface is not a straight line. Generally companies try to take a diagram of the interior shape at the rear of the boot and try to average it out, but there's no real guidelines as to where to put that line. Big calf and protruding calcaneus people will end up with drastically different effective forward leans in the same boot, and so on.

As a bootfitter, you try to weed out the outliers (i.e. flare the cuff for big calves so they aren't at 20 degrees) but for most good skiers it's a case of preferring a stance they've grown used to over the years. Stated forward lean isn't always so helpful, you really need to ski the boot (with a pocketful of different thickness shims) - I like the Lange XT3 LV just fine with no shims and a stated 12 degree forward lean, I also like the Atomic Redster CS Pro with no shims and a stated forward lean of 16 degrees - I went back and forth between these two last year seamlessly, sometimes on the same day.