It's the same negative feedback loop that causes most forms of suppression / shutdown. Basically 4-Andro converts to testosterone, once at supraphysiological levels the negative feedback loop signals to increase conversion to estrogen as a part of the negative feedback loop. This should in turn lower test levels to normal via less the conversion and less LH stimulation at the pituitary.
Right, but his LH/FSH isn't bottomed out. Sure, the LH isn't high but it isn't shutdown either. His FSH looks to be higher than what a stable, physiological T level would represent. Usually these hormones hang out at the lower end but have periods in the day where they are higher.
I think the key word you mentioned above is "supra" physiological levels of T. His T isn't beyond normal levels which might explain why suppression isn't bad. If that were the case, I'd say he needs to double his dose for 7-10 days and retake the blood test to see what happened. Granted, easy for me to say when I'm not footing the bill.
For what it is worth, I'd send some money PayPal to cover the next blood test just to see.
However, I also want to say that LH/FSH will shutdown whether estrogen is high or not. If it were merely just about estrogen/test ratio as the key feedback metric, then steroids that do not convert to estrogen wouldn't shut us down at all. You and I both know that isn't the case though.
There are many things involved in that feedback and generally speaking, whether a wet or dry AAS, the higher the value in the serum blood levels, the stronger the feedback system becomes in terms of signaling shutdown. I personally think the feedback system occurs mainly at the androgen receptors - as we have seen with SARMS - even they cause some suppression mainly because they also bind to the androgen receptor just like traditional AAS, albeit with a weaker affinity.