Radar only tracked the targets -- even when using radar to aim the guns, the gunners still had to set the altitude fuse and aim the shell where the plane would be if it continued on it's current heading.
Because bomber formations didn't change headings or altitude on their run, the rader could be effectively lead right into generally 25-100 88 gun batteries.
Remember that 20,000ft is nearly 4 miles...STRAIGHT UP...there's going to be quite a bit of deacceleration so even at a the 1028 m/s muzzle velocity it's going to take several seconds, factor in vertical deacceleration it's going to be even longer.
88 gunners did try and concentrate due to the low probability of a direct hit, so they kept on projected vectors...if a fighter (or bomber pilot for that matter) changed vertical and horizontal vectors at often enough intervals there would be little danger of heavy flak concentration due to the constraints of the 88mm. Namely though, changing altitude for the most part nullified the 88, even if they did get your horizontal vector right.
Oh yeah, and the 88 wasn't the only large German AAA piece, they did make some bigger ones yanno

- Bessy
[This message has been edited by Jigster (edited 02-15-2001).]