Aux really doesn't matter. It isn't worth the effort, because the margin of distance between two given aux settings is a distance easily covered quickly, far quicker than it is to switch your aux settings.
In other words, if you are worried about staying undetected, then you are better off just flying further away from that ship, not messing with your aux setting. Cloaking as it is lets you get into cannon range quite easily against anything but a science ship, with minimal aux. And once you are in range, why are you still cloaked instead of decloaking, and do you really want to wait for your power to shift from aux to weapons?
Even science ships and Nebulas don't have some godly sight range, it is surprisingly small. The science ship's detection ability is far more useful for catching fleeing BOPs, not pre-detection of cloaked ships.
Again, there just isn't a reason to maximize power to cloak because distance helps you a lot more than aux does.
I run a reasonably high aux on my bop for things like gravity well, but, you shouldn't get too close until you're blitzing in for your strike. Never buff up near your target, the ammount of time you spend near them and cloaked should be as low as possible. All it takes is for a paranoid science captain to pop sensor scan or CPB and the jig is up. So keep your distance until you're ready to go in all guns blazing.
The only time I have relied on this is when I've seen a cloaked ship while cloaked myself. But most things that cloak tend not to run high aux, so I'm almost deffinitely able to see them further than they can see me. A B'rel would be the ideal ship to handle this situation, but any ship can decloak and fire fast enough to capitalize on the golden oppurtunity of an unshielded unsuspecting target.
Also, if you're stalking a target running MES you'll likely have to get close, but this is risky as most ships I see doing this are carriers and science ships, and tend to have science captains.