With an offset tailstock, you have to work between centers not with a part in a chuck. Take the driver out of the chuck and use a dead center in the headstock or in the chuck. Otherwise, you are bending the cue/pin, etc to get it to work on the offset tailstock.
Remember, when working with an offset tailstock, taper is figured on between centers distance, not the work piece.
Butt cap end size minus joint size divided by total length of cue will give taper per inch. Multiply taper/inch by total length between centers, take half and move you tailstock that much from centerline. This will put you within a few .005" of your final taper. A couple of thin cuts on each end will let you know if you are on proper taper. If not, take half the difference and move the tailstock that much and recut. If the butt is already tapered, you can sweep the butt and make sure that the dial indicator reads the same the length of the cue.
In machine shops, taper bars were a high priced item that was not normally used. The lathe manufactuerers rarely made one that would produce a taper longer than 12". Offsetting the tail stock was normally used and a competent machinest can set up a taper, cut it and return to centerline very quickly. The greater the degree of taper, the more pressure is put on one side of the dead center driving the part. The center is usually recut to 60 deg after each part to maintain alignment.
Kenny Murrell