Yeah, well, thay can. I remember having this conversation before, and I still think about what we discussed. To me, it seems like wet highlights will definitely sink down, and disappear into wet mids and lows underneath.
As a result, I have tried a new approach, which doesn't really have enough time under it's belt to fully be judged. But, in the case of some of my latest dudes, I reapply the highest of highlites after a week or so of curing. Then, I hit it again about a week later. I move slow enough for this to not hold me back LOL!!.
That's where these current figures are.
Some of my older figures kinda seem pale instead of dark, but I guess I have tried a new approach to every set I've done. Additonally, I have only been painting figures for a couple of years. So, again, no real-time tested figures. But, I wonder if sealing the figures has anything to do with this fading.
I wouldn't be surprised if, in a year, I have fully moved over to Vallejo shading and hightlighting. Is that where you've moved? I just don't have the acrylic technique down yet. With your heads up to the fading issue, it's definitely worth considering making the transistion.
Steve