I'm building up a few hub geared 20" wheels. The last one I did, given the large size of the hub and the small size of the wheel, a 2 cross was advised, and it worked out well. That was a 36 hole rim/hub. Now I'm rebuilding a 28 hole wheel (gear hub, 20" rim). It was originally done as a 3 cross, but I worry about extreme angles where the spoke meets the rim. I've had failures there before when attempting too many crosses on a hub gear build. But I've always done 36 hole, so now I'm wondering if the number of holes will affect the number of crosses I'm likely to want. It seems to me that less holes will increase the angle of the spokes and therefore make me more likely to want to go with a 2 cross, but I'd love to hear someone else's thoughts. I tend to put a fair amount of weight on my wheels (most of it from the heavier-than-average rider, but I also carry a fair amount at times), so I always try and build for strength. 28 spokes when a I prefer 36 and a 2X pattern when prefer 3X make me nervous. I can't do anything about the spoke count, so I'm just wondering if I should be considering a 3X build, or if my logic is sound in that 3X on such a small rim with a large hub will give me a bad spoke angle.

There's very little difference between 2X and 3X on a properly tensioned wheel. I would go with 2X on a large-hubbed 20" wheel if only to avoid having spokes cross over the head of the adjacent spoke. A 3X places the furthest-out crossing farther out, which makes it easier to interlace the spokes.

I'd go with 2X. Popped a spoke just yesterday right at the nipple on a high-flange build.

go with 2x.
3x is certainly possible if the rims are low profile.

larger flanges spread out the holes more so there's less or no overlap between the spokes at the heads even if the spokes exit at 90° or slightly more. there's no point in getting more than tangent, but as long as the heads aren't being overlapped, it's not a big deal.

Depending on the hub, maybe even one cross for a 20". I've got a Rohloff in a 20" that I built one cross, and it's working out fine. Two cross was going to be too much angle.
A Nexus 8 or Sram 9 doesn't have that much smaller flange than the Rohloff, so if it ever came up, I'm sure I'd do that one cross as well.
On the other hand, I once built a 5 speed Sturmey Archer 36 spoke into a 20", and that one worked OK at two cross.

Excellent. Thanks for all the help. Now I can do my 2X build without worrying about it. There are 2 hubs, both 3 speeds, one Shimano, one Sturmey. Neither of them big enough to force me to go to a 1X pattern, but I've seen places where that's necessary. I laced up a Nuvinci hub to a 700 rim with a 2X pattern and started snapping spokes at the nipple. had to rebuild with a 1X. But I'm thinking these hubs will handle 2X. Especially given that at least one was originally done in a 3X pattern.

One of the features of spokcalc is suggesting an optimum cross pattern.

That's good to know. Where does it show up? I don't see any such value on the version I'm using, but perhaps mine is outdated.