I'm still pretty much a roller beginner, but I find it easier to roll outside too. I think that's because it's natural to push a bit early when rolling to inverted. Push early rolling outside and it helps you move in the "circle direction". Push early rolling inside and you go the wrong way.

Want to cheat a roller? Set the CG so that inverted flight requires no down stick. Then trim your plane via the radio so that it tucks on one knife edge and pulls on the other. Now you can do a pretty good rolling circle with virtually no elevator input required