Alvaro Pires da Silva, Bev Kay, and Ed Perfect (University of Guelph, Ontario) (1994) refined the concept and termed it least limiting water range (LLWR).
The upper limit (wet end) of LLWR is determined not only by water content at field capacity (FC), but also the capability of providing adequate aeration for plant roots (usually taken as a minimum air filled porosity of 10%).
The upper limit is then defined as: min q {air filled porosity = 0.1, FC}.
Rather than air-filled porosity at 10%, LaoSheng Wu from UC Riverside proposed moisture content where Oxygen gas diffusion rate ODR value of 0.2 micro-g/cm2/min as criteria for satisfactory aeration status.
The lower limit is defined as: max q {mechanical resistance = 3 MPa, PWP}.