The 100's are the compact ones.. the other version would be the R200, and they are much bigger. I don't know what significance the 'a' has in that.. and I don't know that the reach can be adjusted on these. I have pretty small hands (my motocross gloves are xxs, my bike gloves are smalls because they didn't have anything smaller), and on my Mixte (which has the R100's) with my hands in the drops, I can reach the levers with no problem. I can't say however, that I really like braking in that position... I prefer to brak from the hoods or from the top of the bars (w/ my cross levers).

You can have cross brakes put on the bars no problem, which may help your confidence a lot.. I have RL720's on both my Mixte and my new (to me) road bike. They're not very expensive.. I paid around $25 for the ones I put on the mixte including shipping, but odds are good most LBS would have them in stock (I didn't check, but mine is a fair drive away and it's not often I can go without dragging at least one kid with me, so it's easier for me to order stuff). Since the bar tape needs to be partially removed to put the cross levers on on, you could have the positioning of the R100's fine tuned at the same time - and you'll want to make sure the cross levers are in a good position for you as well.

I like the cross levers a lot.. you probably would too Some people think they're like "cheating" - sort of the way all the "road" bikes in the 80's had the dual brake levers, but these are different, and work much better... I think I read something somewhere that you actually get better braking power with the cross levers than the aero levers.