handlebar setup query

Experimenting with your setup is key I think.

Also being brutally honest about your flexibility is essential.

While the long and low pro position looks good, if you're not physically capable of adopting that position for extended periods then it's pointless setting the bike up like that.

Once you get your bar height, stem length and bar shape sorted then it's just a case of getting your levers positioned to allow safe use of the shifters and brakes in all positions.

As a 175cm, fairly slim 54 yr old I'm quite happy to accept that I'm not as flexible as I was in my 20's so my bar setup reflects that. I've got a 75mm reach, 125mm drop compact bar on a 90mm stem on top of 30mm of spacers that allows me to use all three bar positions comfortably depending on the terrain.

If I had to give one piece of advice regarding shifter setup it would be that, in most cases, the bars supplied will be fairly generic and the lever setup will be the same. I'd strip the bar tape off and go for a short ride and tweak the position of the shifters. A multitool is all you really need to adjust the position and reach then once you've got it dialled in you can make sure your levers are in the same position on both sides when you get home.

Riding on the hoods is generally reckoned to be more comfortable because you are not so low down but the idea of dropped handlebars is it gives you more positions so can move around for comfort.

On the hoods is also more aero if setup for it as the forearms are more horizontal, that is why you see the pro's on the hoods with a low body position when in a solo break.

The drops give more control and better for braking so that is where you should be on fast twisty descents or when sprinting in a group.

The tops are often used as a comfortable alternative position when climbing and the brakes are not so important.

On longer rides I ride equally in all possible positions as I find I get sore spots after several hours in just one position. I'm equally happy to ride on the drops, tops or hoods, I only struggle when I have my "winter weight" and the extra girth prevents me getting down too low as I then struggle to breath  (I suspect for some of us larger riders out there this could be a contributing factor to preferring the hoods).

I did find it interesting the other day when watching the Tour de Yorkshire and some of the riders even went up hills on the drops, so I don't think there are any hard and fast rules, just ride in the position you find the most comfortable.

My preference has evolved over time. When I first returned to a drop bar bike I rode on the tops most of the time,  only swapping to the hoods when I needed to change gear (I had crosstops so that probably contributed to using the tops). Next bike I mostly rode the hoods, and on my current bike I spend a lot more time in the drops - mainly because I've discovered the lever throw adjustment screw.

So different bikes, different geometries, different positions. All the same nominal frame size so I think the point is that minor differences can change where you feel most comfortable. If a 56 is an average frame size for someone who is 6 foot tall, the most comfortable position for a bunch of 6 foot riders on that bike is still going to vary based on flexibility, age, strength, hand size, and body proportions (i.e. longer arms/shorter legs vs the opposite)

The right position is always the one where you feel most comfortable, because discomfort is going to rob you of power faster than any gain in terms of aero.

I ride on the hoods literally 99.999% of the time. The drops just feel plain weird to me. Each to their own and all that.

I get easier shifting and braking from the hoods, I have small hands and have problems reaching the brake/shifter levers when in the drops. That said I will go in the drops when I feel like it, when it's comfortable (I have gnarly shoulders from old injuries so another reason to be on the hoods a lot). 

As HawkinsPeter says, just go with whatever you feel most at ease with, that is more important more of the time than worrying about what is the most outright efficient body position, and as said, what you think might be more aero in the drops could well in fact be less efficient overall.

I'd estimate that I spend probably half the time on the hoods and half the time on the drops. I find the hoods easier to use, so I use that when I'm tangling with traffic as it gives me better visibility - I'm more likely to be looking ahead than downwards. I switch to the drops when I want to be lower/more aerodynamic which is usually for longer stretches of road and for travelling faster. I could raise up my handlebars to get the drops position as easy/comfortable as the hoods, but then I'd lose my lower/aero position.

However, there's a gotcha in that a lower position isn't always more aero and also being more aero may not be quicker if you can put out a lot more power in a higher position, so being comfortable and enjoying riding is going to be most important for most people.

It's usually because the drops are lower, so you're in a more bent-over position when using the drops and most people find it more comfortable to be a bit more upright (i.e. on the hoods). Maybe you're handlebars are relatively high (more spacers), but if you're comfortable using them, then it's not a problem.