I find with higher speeds I can connect with these features a lot better with a very small ollie.
Shane is so correct. Even with smaller features, anything on a down angle, speed is your friend. A big problem I had was the aforementioned "travelling" across the downbar with 50-50s. I found approaching at a higher speed allowed me to lock on much easier, and allowed me to focus on looking to the end of the rail.
My caution comes for locking in boardslides etc, dont let this habit permeate into your frontboards, back boards etc. When I learned to backside boardslide a down, my back boards quickly turned into backside blunts (aka I would still 'travel' across the rail) , now in a boardslide position. Again, this had to do with where my eyes were looking when approaching the feature. My line of site was over to the other side of the rail, and down at the end. My eyes SHOULD have been just inside the backside of the rail, and down the line where I wanted to land on the rail, not at the very end of it.
I've since solved this problem, and look forward to taming front boards on downs this year (my white leopard trick... hrmmm), but now realise its alllll in the eyes (and speed, as shaner said).