Congrats on the blooms! The lower level of light is causing the large leaves. Your plant's older leaves were formed under much brighter conditions (like in a greenhouse, or outdoors).

Is this a grafted tree? If so, is it possible to take a closer photo of the graft union? Many plants respond to low light conditions by increasing the surface on new flushes of foliage. Mature leaves cannot increase in size, so the plant responds by ramping up leaf size on subsequent growth.

Thanks all! Sounds like a light thing; I thought I was pretty well positioned about 15 feet from a south facing double sliding door set up, but I've moved the tree closer to the windows now.

As for the graft line, I'm not really sure what to be looking for- will there be a line somewhere on the trunk?

15 feet from door/window is like full shade for a plant. In fact right next to a window is not even full Sunlight since the house windows are designed to cut down light and reflect a lot of the light. A Rule of thumb is just inside a window you are getting on the average half the light over a day. Also keep in mind that during winter in northern hemisphere the day length is shorter and Sunlight is weaker than Summer.

When you say '...graft tree coming through...', I think you are wondering whether the rootstock is putting out growth. And no, that's not happening.