One thing that hasn't been mentioned is... undo the stem clamp and twist the handlebars forwards or backwards. As you do this, the angle of the bars at the grips will change quite dramatically and you will detect a change in your wrist angle as you sit on the bike. It will require a degree of experimentation to get the right angle for the grips. Of course, do the stem back up again.
Another thing I always advised many riders taking my classes was to undo the clamps for the shifters/brakes, and move them so the levers are at a 45 degree angle to the horizontal (or vertical if you like). Generally, bikes are delivered from the factory with the levers in a near-horizontal position, and many people ride with their fingers over them, resulting in a sharply cocked wrist. Your hands should rest on the grips so that the line through your forearm and wrist is virtually straight, and yet you still have fingers over the levers.
Seat position plays a role and I tend to agree trying to go backwards with the seat.
As to reach, there is a quick and effective method that involves placing your elbow against the nose of your seat and stretching your forearm and hand to the stem. If your middle finger overstretches the handlebar clamp, the stem is too short (and probably the bike is too small for you). If you end up short of the clamp, the stem may be too long (or the bike too big). There are complications to this measurement, including the backward sweep on the ends of the handlebars. If you want to know more, ask.
And, improve your core strength, and particularly your stomach muscles by doing a regular set of sit-ups/crunches.
Much of this sort of fit issue is a process of elimination. Try one thing and one thing only at a time, and be sure to mark the original position of any components you change so you can return to that position should the problem not be solved.