anyone able to point me on how to adjust my grip shift?

the front derailleur is not being moved far enough over when i am on the 2nd pedal sprocket, so the chain is rubbing against it when i am in gears (rear) 4-6 (same situation for 3rd sprocket too).

i think i know why, if you look at the attached image, the twist shift is clicking before it gets to the "2" marker. if i twist it further until it is lined up with the "2" then the derailleur is in the correct position and the chain doesn't rub.

so from the looks of it i need to adjust the twist shift so that it locks in the correct position?

So, all is well in the big chainring?
When you say gears 3-6, how many gears total are on the rear?
Is it rubbing on the inboard or outboard plate of the front derailer?

yes all the gears work fine.
18 gears in total (3 x 6).

when in 2nd big gear, small gears 1-3 are fine. it's only when i move into 4,5 and 6 that the chain starts to rub on the front derraileur.

if i twist the grip until it lines up with the "2" mark then all is OK with no rubbing.
the grip shift is clicking and locking too early, so i think i need to adjust it so that it clicks and locks at the correct point.

This would likely require some machine work, possibly molding some new plastic bits for the interior of your shifter. Perhaps SRAM would replace it for you if it's found to be a manufacturing defect.

Was it always like this, since the bike was new? If not, perhaps a little more cable tension is needed.

Does your shifter have a knurled adjuster where the cable exits it? While standing on the drive side of the bike, turn that adjuster counterclockwise a couple of turns and see if that helps. If it helps a little but still not quite there, try a little more. If adjusting this totally wrecks your shifting, I'd suggest a bunk shifter. It kinda looks like one that comes on $150-300 bikes, so QC might not be that great.

yes. i just assumed that the cable needed adjusted or something similar.

If increasing the cable tension seems to help a bit, but never quite gets there, try resetting the cable in the derailleur.

1. Screw the adjuster back in as many turns as you've unscrewed it.
2. Follow the steps that start at approx 2:20 in this video.

IS that shifter indexed or has micro adjustments allowing for trimming of the front derailleur?