Hey there Dr Dave!
The mazzer is a great grinder though does have its idiosyncrasies. 2mcm recommends that when dosing the PF, give the lever a good, hard thwack - this reduces the problem of throwing to one side. I still tend to place my PF off centre and pretty much accustomed to it now and no longer have coffee spilling everywhere. A large sized coffee matt to replace the dodgy plastic thing that comes with the mazzer is also a good option.
As for the spray in the doser...I tend to find that this can be very dependent on variables like, grind, bean type and grind setting. Whilst a fine grind can fall out in clumps, if you are grinding something like monsoon malabar through the same setting it sprays all over the inside of the doser. Bottom line is that I dont think it much matters about the coffee dropping into different segments. Once you start thwacking it will pretty much clear this out anyway.