I do not have the ES4 Designer handy any more but used the AEM Forms 6.2 Designer.
Which 2D Barcode object did you use exactly and what is the data length (in characters)?
Here is an example with the QR Barcode 0.625in with different data content:
10 chars:

50 chars

101 chars

102 chars

Due to the limited size you can only bring in so many characters before the barcode has not enough space left to grow. That differs from 2D barcode type to type but all have limitations.When you turn error correction off (0) then you can fit more characters at the loss of the correction (about 135 or so).
The fact that you can only reduce to 0.8317 in is probably due to the amount of data you fill into that barcode.