Yep, you’ll need to avoid any rolling of the stones at the transition point to avoid rounding that point over. As Mikedoh says, treat the edges as if they are completely different. This could mean re-mounting the blade in the vise so as to put the Tanto edge in a horizontal orientation. No sweet spot required. Actually, any clamping position that puts the edge(s) where you can get at them is OK. For any relatively straight edge, the angle will be constant regardless of whether the edge is actually horizontal, relative to the vise. Even if it’s at 45 degrees, the sharpener will produce a uniform bevel angle. This means you could, for example, clamp the blade with the Tanto corner well above the vise, with both edges at dissimilar angles. In this arangement, the Tanto corner would be offset to one side of the vise.
Am I confusing you? Sorry… It’s really late and I need to go to bed.