I only put the scope where my head is comfortable. That's purely what drives it. The click or so per 5 yds I save is really immaterial to it as being the driving factor.
I start with a rig setup around the sitting position. I start by getting the gun as low down as possible, so i'm not using a hamster which jacks the centre of gravity up. I then remove the cheekpiece entirely, then place it where my head wants it to be. Once there, I then stick the scope where my eye wants it to be. Only then once comfortable do I play with hamsters. Much easier to do on an alutec style stock.
The main dimension of interest is the distance from the bottom of the stock where it sits on knee/hand, to the scope's bore... that is what you're looking for. Whether you jack the barrel/action up to the scope with a deep hamster or use a high riser is up to you. But around 3-4 inches you start to run into issues like scope travel, and also standing becomes more problematic, as in reality you want less distance between your support point and the scope for standing... so you can get your arm vertical and the weight carried down through it's bone, not using muscle to lift or hold the rifle up.
Granted I'm not using the stock I should be... i've been procrastinating a new stock for years now... but i've done this with other shooters who seem to find it more comfortable.
With FT though there is a compromise. Sitting is 80% of all shots. But it depends if you want to chuck your strengths into that, or slightly weaken that setup to be stronger for a weaker position like kneeling or standing.
You'll see from the 3p boys there is a considerable amount of difference in the stock shapes between the one end of the spectrum, standing, and the other, sitting... sitting tends to be deep distance between scope and hamster, long butt... standing, short butt, shallow distance. Kneeling somewhere in between. The 3p boys have different hooks, cheeks, fore-ends for each position, all set up ready to go... but they are shooting at fixed distances at fixed heights. With FT we need to be more adaptable.
Also weight plays a part. A good place to start is having the CofG over the support point. With sitting that's further forward on the rifle than standing... not to be confused with where people end up supporting the rifle in standing, because you naturally move to support the CofG, not change the rifle to where it should be supported. With standing, the CofG is more commonly much further back.
As with everything, the more you pursue perfection, the more it needs to be tailored to the individual circumstance.
One thing I would say is having good core strength and the ability to get your knee closer to your chest, and stable, is quite key... although there are several large shooters who buck the trend, there's a common theme with most of the top shots. I don't know how the large lads do it. I put 1.5 stone on and really started to struggle... and I know those with hip or back issues who can't fold themselves up so well tend to end up with large distances from hamster to scope bore.
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