seems as if the problem was two-fold (as I had sort of suspected), grind and dosage level.
For dose level, I fill the pf, tap a few times, refill then level off, tamp. The entire steel from the SB tamper is under the level of the PF, so its quite low in the basket. PF locks in just past 6 oclock.
Grind is quite coarse, runs just on 20 secs on the 6910 at home but gives quite a good 25 (ish) sec pour on the Ikon at the shop and gives good crema and colour.
Have found the ikon also seems to like being surfed. Run some water through the group and stop, re-do it again to get the boiler filled, wait till its stopped heating then run the shot. Dont have the patience to try various time from the finish of the boiler cycle, but it would be about 15 - 20 secs by the time I get things sorted out to run the shot.
Its certainly not a set and forget machine with a very different approach required than the 6910 at home.
The joys of this obsession