Drift Roses not growing at same pace

I planted 12 drift roses in front of my house last summer. 6 on each side of my front porch. The ones on the right side are 2x the size of the ones on the left. The roses actually get smaller as you go from right to left. The right side can be exploding with flowers while the left side barely has any.

The front of the house faces south and gets full sun all day. There is a wooden fence a few feet to the left of my roses on the left but I don't feel like they block much sun. I cannot figure out why the left side doesn't grow light the right side.

Thoughts?