It sounds like you’ve really made good progress with your aerobic base. You are correct to have been adding more intensity. The best rule of thumb I can give for adding intensity is: Add intensity volume until you feel like you need to reduce the Z1 volume because of poor recovery. If Z1 is feeling too taxing you must reduce the intensity of those sessions so that the high intensity session are not negatively impacted.
I agree with your assessment of AeT in the low 160s.