I like to suggest that the riding position does not define flat bars to drop bar preference.
Like many above post, I use the hoods most of the time and Aerobars against the wind.
I have set up my riding position at about 45 degrees for hoods, aerobars and flat bars (with aerobars).
It is possible to lay almost flat with my back if I slide back on the saddle using aerobars against strong wind.
The advantage of flat bars with T-ends and aerobars is on very bumpy road or trail. Gripping wide on the t-ends gives a lot of leverage which I do not have with drop bars.
OTOH, drop bars tuck you better in aerodynamically. So if I do something like a TT or PB I use drops. If I go on a bumpy road or trail I prefer straights. I have both. I find both comfortable for century rides provided I have aerobars.