Late additions of citrus zest and spices?

So, I've been pouring over my notes as I review my 'year in beer' and one thing I've noticed is that any additions of spices and or citrus zest added at 10M, 5M or flameout are basically indetectable in the finished product. For instance, I did a spiced clementine porter recently where I added the zest of an ENTIRE BAG of clementimes to my flameout addition. Shockingly I cannot taste the citrus at all. Additionally, I added a whole ounce of cracked black peppercorns to a recent beer at flameout and it is just not there at all. This suggests to me that adding these items at that point in the boil is just not effective.

Therefore, should we be sticking to adding these additional flavorings in secondary? I would be curious to see if other people are having similar experiences.

That is definitely not my experience. 10 minutes spice additions definitely come through for belgians etc

It's really going to come down to the beer, for example, your porter may have just been a little too comes in other ingredients that over powered the spices or whatever. Some elements also fade quite a bit when stored for a long time.

IME, lighter beers benefit from late additions and darker beers benefit with the secondary and longer times conditioning.

It will depend on your beer...super hoppy ales or malt bombs will mask most of the flavors. I have moved all my spices and zest to either 5 minutes or flameout with a steep. You can always make a vodka tincture of you spices or zest and add it to the secondary/bottling bucket/keg to get a more upfront flavor and aroma/