A spice grinder is a terrible way to grind coffee. You will get a very inconsistent grind size, leading to inconsistent extraction (the smaller grinds will become over extracted much faster than everything else while the big ones will be underextracted), leading to awful coffee.
The advice offered here is generally pretty good and given for a reason - there are few shortcuts to good coffee!
Ha! I've just bought the em7000 and use the breville smart grinder too. I just spent 90 minutes and 20-30 odd shots to come up with the same combo as you've said, 7/8 onthe grind and 18-20 sec time, give approx 19gms of coffee.... wish i had read more first!. I'm finding the pressure gauge is quite 'tamp' dependent too - hard to keep the tamp pressure consistent, c.f dose, grind etc... If i want less coffee, ie 16gms, should i use a courser grind? it's late and im getting confused....
To achieve the same flow rate a lower dose needs a finer grind