Hunt coats are really
hard to size without trying on... different brands fit very very differently! And what looks good on one person doesn't necessarily look good on another. Is there a tack shop around that you could try a bunch on? I'm 5"2ish, generally wear a size 4 or small in most clothes and a 34 in show shirts. My jacket is a size 12 and I've found I'm a 12 (or a 4) in most coats. I'm not particularly long armed or waisted or anything so I'm a regular, not long or short.. Anyways. My coat is an Ariat 12. Ariats tend to be a bit boxier then others (i have big shoulders). Grand Prix I think tend to be very small in the waist and then flair out at the hips. I have no waist and no hips so they look terrible on me but fantastic on others. Elites are more slim cut then ariats but not as curvy as the Grand Prix. Tailored sportsmens fit alot like Elites. RJ classics have several different models. Most of their more 'affordable' jackets are a little roomier and get more tailored the more expensive they are. I actually work with a tack shop from time to time, mainly helping people find properly fitting show clothes so making sure people get the right show clothes is a "passion" of mine
.What you want is your shoulder seam to hit right at the edge of your shoulder, for your waist to be fittied, and the bottom of your coat hem to hit a touch above mid-butt. Sleeves should allow for a tiny bit of shirt cuff to peek out when your arms are in riding position. It should be fitted, but not so much that you can't release without popping a button! I hope that helps a bit. You may want to just order a bunch of coats and return what doesn't fit.