Agreed, unless you are noticing a significant tonal change between strings its not something to worry about. In a lot of ways it would be similar to the variation you might get between plucking with your ring and then middle finger. Unless you have a strange plucking technique, your middle finger pluck is always about a centimeter closer to the bridge and I doubt very many people worry too much about that difference.
+1
The only time I've noticed any audible issues related to the angled bridge, was while recording some short tracks to evaluate string changes, etc., on my ABZ.
I was trying for perfectly repeatable samples, and found myself using the edge of the pickup housing as a guide, in order to make my plucking position more consistent. Otherwise, I could convince myself that the one string was slightly darker or brighter than another, just because of minor inconsistencies in my right hand attack.
I've never noticed this as an issue under normal playing conditions. In fact, I guess I approach bass lines like a singer, unconsciously adjusting my "breathing" (right hand attack) as necessary to get the sound I'm after.
To that end, I will pluck, thump or fan the strings anywhere from about the 9th fret up to about an inch from the bridge. When your right hand is moving around that much, a centimeter one way or the other isn't going to make much difference.
The ABZ's sensitivity to these antics, is one of the things I love about my Dingwall. I can get a sweet, round attack on the skinny strings in the upper register one moment, and then an angry grind the next, without touching a knob...