A bit of side topic: I wonder if how often you in particular have been cutting back your quince is the reason for it's smaller leaves and short internodes. How much cutting back are you doing on it in a season?
I have not cut it during growing season, just in Fall after leaf starts to drop and Spring after flower drop.
First cut was late Fall when received, thought it was a clump, and it was very leggy. I cut back everything to 6 - 8 inches including 1/2 dozen or so suckers that where so heavy made the plant seem to be a fat clump. Originally they were roughly all 15 to 16 inches. At that point I also did a simple up pot to the 2 gallon Nursery pot, half filled with crushed slate.
Second cut was the following Spring after flowering. I did a lot of digging and removed all the suckers. I also took a short piece of 2 - 3 inches off of the 5 remaining branches.
It grew well but had offered little or no ramification, those branches grew a minimum of 8 inches, some 10. Gained 3 -5 smaller branches. but Internodes were very tight.
Third cut was last Fall, I chopped all of the 5 original branches in half leaving them 6 - 7 inches or so. It came back with an a additional 19 branches so I am looking at a minimum of 24 possibly more to cut back in a few weeks. I guess it was finally established.
I did another round of partial defoliation last week, third one this year and it is tossing more leaf out on areas I cleared out. It throws an occasional flower out randomly as most Quince do. The last one was at the base of the trunk which I found odd and that same spot now has a leaf cluster to be removed.
Fourth cut will be when I start seeing normal leaf drop. I will be cutting each branch old or new back to and into old wood as it seems to like that best.
Rigorous grower here but my medium and grow methods are different then most. Anyways that's what has worked for me some years ago and seems to again. I am currently working on other varieties and will expect the same growth as in the past, also adding a few more as they become available.
Here it is since I cut off a few hundred more leaf - about 30 percent last week, early for me(off center, etc...) but a fresh picture complete with morning dew a few minutes ago -
Another picture showing where new leaf is already repopulating old wood in 6 days -
It is 13 inches tall from the soil line, but the trunk is buried at least and inch along with the surface roots for Winter. 22 inches wide at he widest point.
Grimmy