Bug-fix in gmnl_2a model -- negative correlation between phi and tau was not correct. Phi portion was explicitly calculated as '1 - tau_portion' so when tau portion was negative, the code would incorrectly boost the phi amount/amplitude. Now basically doing '1 - abs(tau_portion)' for the phi_portion.
The, theoretically, "valid" range for the aforementioned correlation coefficient is still from -1 to 1 (not outsied thereof), but more flexibly values are currently allowed, purely for experimental and testing-of-robustness purposes (will, most likely, be deprecated in near future).