Sanguinelli Citrus Grafting/Pruning Question

First off, I'll admit that I'm almost certainly being excessively fearful about cutting off a limb of one of my beloveds, but it's not something I've done before, so I'm asking this on here for some level of reassurance.

A little over a year ago, I bought a citrus sinensis 'Sanguinelli' from Logee's, and while the plant has been attacked a bit, it has survived. That said, the branch coming out of the lowest part of the plant has leaves that are bigger than the ones coming out of the upper part.

Okay, so I expect that means I should chop off the lower branch, but a couple of things give me pause: The branch was there when I received the plant, and for the life of me I can't seem to figure out where exactly the graft line is, if the plant is indeed grafted.

The picture is the stem of the plant, with the thicker branch being the one I think I don't want.

A picture of the entire plant:

And a baby picture:

Something to keep in mind is that leaf size can change in response to the amount of light it's getting. The less light, the larger the leaf.

As small as it is, it's possible it's not grafted as all. I don't see a bud union either, and they're usually pretty visible.

You might want to email Logees to see if they can tell you if it's even grafted. I saw no mention either way in their catalog.

I agree on asking Logees--I suspect they probably grew it from a cutting rather than grafting but I'm sure they'll be able to tell you for sure one way or the other. But I don't see any signs of a graft there between your bottom branch and the one above it, so I suspect they are the same plant.

"If your recieved the plants from us then the Sanquinelli blood orange is grown from cutting so there is no under stock issue. The larger leaves can be a result of growing under lower light.
Logee's Customer Service"

Thanks for everyone's help and advice. I'm glad I posted rather than chopping it.