I take it that the view that there can be no dead ground is that the crew would load canister at close range and the canister would burst inside the barrel, hence there is no "dead" area in front of this hail of canister balls from the moment they leave the barrel.
I have noted some sources argue that the canister was not intended to burst inside the barrel. Rather the canister was specially strengthed so that it withstood bursting until it struck ground some distance in front of the gun. One source that notes this is Otto de Scheel (ie Memoires d' Artillerie, 1795).
The Russians seem to have a canister which was packed with gunpowder and had a fuse. In effect a shrapnel type round which exploded (if not already burst on impact). This appears to have been intended for the Licorns (I'm not sure it it was suitable to be fired by standard cannon). This originated sometime in the 1750's but I have no details if it was in use during 1795-1815. However I have a note that Kutusov indicated canister should only be fired at somehting like 100 metres or more. (I don't have the full details it was provided in email in passing with a Russian speaker)
If this is the case then there is some 'dead' ground due to fuse( Russian)or first strike (French)ammunition.
Certainly it makes no sense to make canister out of steel or iron with solid wooden bases if it was intended to burst in the barrel. In such a case a light wooden base with a canvas (or similar) bag to hold the balls seems a better option. In effect the least amount of resistance to the dispersal of the balls.
One the other hand if the canister is so strong then why can canister not be fired out to longer ranges. Just as a cannon ball could eb fired to a first graze at say 800m then why not a canister?
Has anyone got any more insights on this?