It's kind of tough to comment on bike fit by pictures. What I can say is that if you are comfortable and have been fit by a qualified triathlon bike fitter you should be okay. Not every fit is the same and not everyone is going to be horizontal on the bike as it is a pretty aggressive posture some are not capable of given their fitness level, height, weight, bike size, or ability to bend that way. Look at some of the pros, not all are horizontal.

For what it's worth, I have been told by the guy that fits me that comfort is key for long races and he'd rather me be a bit less horizontal if I am comfortable, able to breath properly, and able to do the 100 plus mile rides comfortably with the power needed to have a good race and save the legs for the run.

Good luck dialing in your fit.

x2
Comfort is king. Seems like if you lowered and pushed the seat back you would get too stretched out and lose your 90 degree elbow angle. I am NO expert though! Good luck!

The longer the distance the more important comfort becomes.

I don't think it's possible for you to get too stretched out on that frame... top tube doesn't look long enouhg to allow for that. But I'm afraid that if you slide the seat back to get flatter you'll end up with your knee fairly far behind your pedal and may loose some power.

That said, tape's a wonderful thing. If you want to play around with your fit, go for it. Just mark where you were before so you can get back to where you started.

the main question with bike fitting is this...are YOU comfortable in that position for long durations of time looks to me that your aero bar angle needs to come up a little more so that your fore arms are slightly angled up this will drop the hieght of your shoulders just a bit and make for a more comfortable riding postition...have fun

Go get a bike fit. Don't mess around with guessing especially if you are doing HIM/IM distance