I'm not a fit expert but I am constantly immersed in discussion with team riders about fit and I recently went through a comprehensive fit with a guy who contracts out to a lot of higher end LBS and works mostly with racers and customers who are getting a high end custom. He's a Serrota certified guy ...blah, blah, blah... he knows what he's doing.

He says the difference in saddle height and bar height should be measured in a few cm ...not inches. So in short, your bars are too low and when in the drops you would naturally slide forward. TT or Tri bikes with aero bars are the exception because your forearms ride above the bars.

If you have long legs compared to torso length, then your head tube length is too short because you went with a smaller frame to get the top tube length right. Stacking the under the stem and over the head tube to raise the bar isn't ideal but a solution. Although, it may require a new fork with a longer steerer tube to make this happen.

Also, he said that the most common fit error he sees cyclists make ...including the very experienced and racers is saddle height and cleat position. Usually the saddle is too high and the cleats are too far back on the shoe. Maybe you could revisit the saddle height?

Here's a guide for saddle height that will get you to a reference point that you can tweak to within millimeters:

Stand with your back against a wall, your bare feet 6" apart on a hard floor, looking straight ahead. Place a book or carpenter’s square between your legs with one edge against the wall, and pull it up firmly into your crotch, simulating the pressure of your saddle while riding. Have a helper measure from the top edge of the book to the floor, in centimeters. (You can convert inches to centimeters by multiplying inches by 2.54.) Repeat two or three times, for consistency, and average the results to get your inseam length.

Then... you’ll be able to set your correct saddle height, which will be within a centimeter of .883 x inseam length, measured from the center of the bottom bracket to the low point of the top of your saddle. This allows full leg extension, with a slight bend in the leg at the bottom of the pedal stroke.

LeMond recommends that you then shorten this length by 3mm when using clipless pedals. Also, you might consider a slightly taller saddle height if you ride with your toes down and your heel raised. Most importantly, make any changes in saddle height gradually, and give your body time to adapt to the new position.

Good luck!