I have been messing with regs now for some time. I imagine in the last year or so I have made the most progress. This progress is as a result of Paddy O Hares advice to me on where to tie the regs/drone stock into the bag. Now I moved mine but its still not perfect.Being able to reach the regs is a major factor and it seems to be dependant upon where the drone stock is, where the air stock is and also the length of the hose on my bellows.
Is there anyone out there with a sure way or plan on where exactly these should be tied in and what sort of things a piper should do ensure maximum reach? Any advice(s) would be welcome.
The only certain way to get the stock in the right place first time is by trial and error!
No, seriously though, the way I have done this in the past, and shortly will have to do again for another piper, is to make a mock up bag out of heavy cardboard. I do this by inflating the bag after corking all the holes, and then drawing around the outline of the bag keeping the marker pen perpendicular to the edge of the bag. When you cut out this shape it will correspond to the full bag. Then you cut a square hole around the area where you think the stock will tie in. Now take some more of the same cardboard and make up a larger square then the one cut in the bag template, with a hole in it to take the main stock. Then all you do is, using some duct tape (Gaffer Tape?) to temporarily stick the square holding the mainstock to the template, with the template in your usual playing position. If you are really dedicated about this you can also attach your bellows blowpipe to the template to make sure everything is adjusted properly.
You just move the stock around until the position is right for you. Once you are satisfied you can then transfer the hole position onto your real bag.
The good thing about this is that you can have as many dummy runs as you like, and also experiment with other pipers preferred stock position, i.e. Paddy Keenan’s, where he has his stock very low and thus the regulators lying virtually flat, or the other extreme, as graphically demonstrated by the lovely old lady on Ebay, where the stock is happiest over her shoulder. 
Never heard of the above method, but that sounds interesting. Another cheap option would be to get some vinyl and make your own bags, experimenting with tieing in all the stocks. I guess the downside to that option though, is that you only get one shot at tieing everything in… But vinyl is cheap anyway. Paddy Keenan likes the vinyl bags anyway.
You also have to remember that accessing all the keys also involves moving your body and/or your leg. I can play the C,B, and A on my bass reg with my right hand thumb without moving (while still keeping both hands on the chanter that is), but if I want the low G, I have to swing my right leg to the right an inch or two, and voila, it’s right under my thumb.
If you use a strap to keep the stock suspended from your left shoulder, you can change the length of the strap, but also, you can move the left shoulder in and out to help reach the reg keys. This, plus swinging the right knee back and forth as bensdad suggested, should give you better access to all the keys.
djm
A properly fitted bag should enable all regulators to be played without the need for contorting the body.
The posistioning all depends how the piper likes the pipes to sit and then stock placement and the bag length should be taken into account
Sorry and the height of the piper should also be taken into account ( Thanks michealloos) 
The piper’s length should be taken into account as well.