If you use an UNUN, you may very well have to change the taps. Although not deal, you can wind a shunt coil for the base of the antenna, and get the SWR within reason (<1.6:1) on 8 through 10. The coil needs to be about 1 uH. I use one that is 1.25 inches in diameter, 8 turns, # 14 Thermalese. The inductance can be changed by stretching or collapsing the windings.
You didn't say what sized coil you were going to use. If you use too large of a coil, say 6 or 8 inch, there will be a difference in performance from 17 up. A good compromise is a 480 from TBC.