By way of qualifying what I am about to suggest I will first tell you that I am currently a qualified bike fitter for both road and TT and formerly a six times National TT champion spanning the period when Tri-Bars first came into use in the UK.
It is impossible to give specific measurements for adjustments without doing a full bike fit which involves a physical assesment to establish such things as flexibility, range of movement in key areas and left to right symmetry.
However, I would advise some simple changes to start with. First find the mid point of your saddle (front to back) and from this measure down to the centre of the Bottom Bracket to establish your current seat height (which may well be incorrect though!!) Then move your saddle forwards as far as it will safely go on the rails (it is currently set very far back). Once done check the saddle height from the mid point to the centre of BB and adjust (up) where necessary. It will definitely need moving up if you have moved it forwards.
Next remove all the spacers from under the handlebar stem and drop the stem down as far as it will go. I would suggest initially put the spacers back above the stem before cutting the steerer tube down, as once this is done there's no going back!
Next, if your Tri-Bars will allow, fit them so that the arm-rests are either behind the handlebar or on top of it, but not in front. If not possible then you can achieve the same by fitting a shorter stem.
Next, raise the front of the Tri-Bars so that they are angled upwards slightly. This will give you a smaller more closed-up frontal profile. Think of the position adopted by Downhill Skiers (which is where the original idea for Tri-Bars came from) Much more aerodynamic.
Next, train, train, train, in this new position. You have to be used to it BEFORE you start racing in this position.
Next, enter a Time Trial, and do a PB - EASY!!
If none of this works, try Golf. Seriously though, if you do get serious about your time trialling then it is money well spent to have a proper TT bike fit which should take in the region of 3 hours to do properly and will give you massive benefits.
Hope this all helps.
Graham