small pith shouldn't really make that much difference. i usually cut right below the node and try not to damage the node. usually, there is small pith/white stuff, but so far not much of an issue. at cup stage, lot of the issues are due to giving it water. if humidity bin is being used, more than likely pre-wet soil mix will last for a month or two before watering is needed. if humidity bin is not being used, the watering becomes tricky. if you water too much, you can kill the cutting. if not, you can kill the cutting. some people have it down to science, i haven't gotten to that point yet. but i know what works for me.. that's the thing with rooting the cutting. something that works for me might not work for the others. and what works for others might not work for me. have to try and find what works best at your location.