After re-reading that paper, I updated (only) the parameter labels on the OTL above.
So: Elastic Modulus - the strength of the elasticity effect
Plastic Yield Limit / formerly Gamma - the strain limit at which plastic flow occurs. A high value means little plastic flow (fluid is mostly elastic and always tries to return to original shape), low value means plastic flow can occur when norm of the strain matrix (think total deformation) is above this limit.
Plastic Flow Rate / formerly Alpha - how quickly the fluid will flow when strain is beyond the yield limit. A low value (or zero) will imply mostly elastic behaviour no matter the yield limit; a high value means the fluid will flow quickly once past the plastic yield limit.