Thanks for the tips, gents. My painting has gone through cycles, I started with no primer (lol), then I moved to using white primer, next with LoTR paint articles in WD, I was persuaded to use black primer... then paniting some WWII stuff, I chose grey primer. All the time using the traditional base coat, wash, highlight.
Now again, I've been experimenting with zenithal priming, and contrast as I said. Oh, and I've started dabbling with oil washes too, inspired by that Marco (not just mecha) guy on youtube. He makes it look oh so easy.

So I guess I will try out zenithal, just have to be real delicate with my airbrush action, so as not to flood the mini with white...

I will swap a smaller nozzle too.