I think bomb accuracy should get worse the higher up the bomber is. There are more variables at play and hence the "spread" should be bigger. I believe that currently there is, or at least there seems to be, a penalty for dropping ords at high altitudes. I notice this when I drop the 50 kg bombs from the He111 on the city at the strategic complex (6 bombs on each city block). The spread seems to be bigger at 20,000 ft than it is while at 10,000. Not much, if any, but there seems to be some.
I'd like to hear HTC's comments on how altitude affects bombing accuracy, if at all. Hearing it straight from them is always better.