It very well could be working fine on the 13" small formats (other than the 1430 which has a different head) as QTR uses a different dither/microweave compared to the larger cousins and also due to the 1.5pL dot size vs the 3.0pL dot size (which spreads out more). I admit we did not test after testing 10 or 15 different films variations on the large and only getting Ultra to work properly (density-wise).
To keep it simple we say that Ultra is required so nobody goes buying paper they can’t use when just starting out, but if it works, it works! No worries!
best,
Walker