Gotcha. At least run it a few inches under the tape. And tape the housing directly to the drops, then wrap over everything. Having the cable taped down will keep it from flopping around as much. I dont think, in my mind at least, that the cable should run immediately from the shifter down to the downtube cable stop as the bend will be too severe. Of course this is what I am picturing, so it may be different on your bike. A gentle sweeping bend is best, so running it at least a few inches would probably be best. The more then better, up to the bend in the handlebars though, since that will only further secure the housing and reduce the chance of a snag pulling anything apart.