Bill
The info I'm giving you is from the prospective of the X-Terra 30, so the numbers won't line up exactly with the 70, but will still give you a good idea on what's going on.
Unfortunately the 2 targets that present the greatest challenge for modern Aussie coins, are pull tabs and screw caps. There isn't a single detector on the market that can separate these targets via a numerical value or a separate notch.Not even the Explorer. Yes it can separate most pull tabs by a single value in perfect conditions, but often still show up as a 10c piece.
What you need to do is look for other ways of figuring out these targets. The simplest indicator is that on the X-Terra 30 a 5c piece will give a solid 8 while a 10c piece will mostly lock into 12, with an occasional bounce to 16. Play around with your X-Terra 70 to see where they hit on it. If you go after targets that behave like this, then it will reduce the amount of pull tabs that you recover. What you will notice with pull tabs, is that they generally tend to make the numbers jump around. In standard pinpoint, if a 10c piece is just under the surface, then will give a louder pinpoint than a pull tab can. You may what to play around with the prospecting mode, just to see what differences you may be able to hear with that.(ie. on a couple of detectors, in the right conditions, a pull tab can give a double beep if you pass over it in one direction, but when you pass over it again at 90 degrees, then you will only get a single beep. A coin will always give the same number of beeps in both directions.)
If you are hunting on a beach, then dig all of your pull tabs, as some of them will be ladies gold rings.
Have fun.
Mick Evans.