Hi Bula,
You seem to have got some real, current pilots on the thread since my request for more data. I retired 11 years ago, and most of my 14 years' A320 experience was on CFM-powered A320s, whose MSNs were in single or double digits.
However, after many years we added a bunch of A319s with the IAE engine, while retaining the old A320s.
Flying both types regularly, my impression was that the A/THR-engine combination responded slightly better to windshear on the CFM A320s than the IAE A319s. But the A319 needed less thrust on the approach, which could have made a difference.
What I was trying to establish was if you were likely to have been carrying any extra speed due to GS-Mini prior to your "undershoot shear" (never heard that term before, but think I've got the idea now). If you were, that would make the sudden loss of height unlikely without a substantial downdraft.
You've given me a great clutch of winds, but at what height did you have the shear in question? 600 ft, perhaps? What surface wind had you entered in the PERF page? Finally, roughly what was the minimum speed relative to (a) managed speed and (b) VLS?
BTW, my practice when visual was to disconnect the A/THR if I wasn't using the AP. The throttle levers are a joy to use, and GS-Mini is a great tool, provided you use the constantly-changing managed speed as a target, not a minimum speed. On the other hand, the A/THR device whereby you can add a burst of thrust by briefly pushing the levers beyond the CLB gate can get you into a lot of trouble, IMHO. Not all airlines permit manual thrust (yet...), and I agree with USMCProbe's sentiments on that issue.