Another thing that affects the action over the whole neck on a strat is the neck angle. Strats have a bolt on neck so you can remove the neck and add a shim (e.g. a thin piece of card) to change the neck angle (in fact I think some may even have an adjustment screw) . You should be able to find good guides online, but I believe the various adjustments/effects are:
Neck angle - this will affect the height of the strings high up the neck.
Truss Rod - this will affect the curvature of the neck. If strings are too high specifically in the middle of the neck then the truss rod may need to be adjusted to relieve some tension and let the neck straighten.
Bridge Saddle Adjustment - you can also set the height of the strings at the bridge - and you'll have to shorten or lengthen the strings by adjustments here to ensure that the intonation of each string remains correct.
Nut - not normally a problem but if you have heavy gauge strings they might be sitting too high and the nut may need adjusting (filing to make the channels wider/deeper).
All the above will interact so if you change one thing then all the others may need to be adjusted slightly too. I'd only do this sort of thing on an old guitar until you get confident. Better to take it in to your local music shop and get someone with experience to set it up how you like professionally.
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