I have the RJ breeches (I think the ones you posted about - I'm the one that got the tag info for you ). I normally take a tall/long if breeches are low rise b/c I'm long in the waist. The RJ Platinums that I have are a low-rise regular, and I find them pretty low. I can wear them with a shirt tucked in but they do feel a bit like my butt's going to pop out. They really aren't that bad but I'm used to wearing the waist of my breeches just below my navel.
I've spent most of my life riding horses. The rest I've just wasted.