If you're jumping a canopy that's huge for you (relatively speaking), the container would have been made to accommodate the canopy size, which could have a wide yoke.
My pin-closed rigs (Vertex's) have fairly narrow yokes - one holds a 185 VTEC and the other holds a 205 VTEC. My velcro-closed rigs (Reactor's) seem to have slightly wider yokes, with the widest one holding a 220 FLIK.
You can try cinching your cheststrap tighter after you gear up, which is a bit more effective if you have an articulated harness (rings at the hips allow the main lift web to flex inwards a tad more than non-artic). To be comfortable doing this, put the rig on, hike it up on your shoulders to where's most comfy, then tighten your cheststrap in that position, followed by tightening your legstraps last. Just make sure that you feel comfortable with where your BOC is situated, as it could end up being a couple of inches higher than before.
I don't think packing really has a huge effect on how the yoke fits, unless you pack really 'fat', which could make the rig fit tighter overall, causing the backpad to push against your back and pulling the yoke & riser area outward.
For the most part though, dealing with wide yokes is just part of being a small person. Although I'm taller than you - 5'1.5 .