Nick,
See the two sites, the BundesArchiv may be able to help if there are records held of reports to Ob.der Luftwaffe on luftwaffe activity in the period
http://www.feldgrau.com/contacts.html or
http://www.lexikon-der-wehrmacht.de/Suche-R.htm. The KG6 history 'Wir flogen gen Westen was written by Jan Horn, who I believe is at present working on another unit history. He may be able to help but I have no contact with him, others on TOCH may be able to advise you on contacting him.
Going back to Petworth the main bomber units attacking the UK in the period were KG2/II/KG40 with Do217's and KG6 with Ju88's. Both have unit histories the KG2 book shows nuisance raids by 22 aircraft of 1X Fliegerkorps on the 28th and attacks by aircraft of KG2 and 6 on the 30th. The KG6 history has both these attacks but adds the 29th. as an attack by a few of their aircraft. The chance that KG6 was the only bomber unit operating on the 29th is added to by a Fighter Command appreciation report ( held in File AIR16/236 at the PRO Kew ) which states ' 29th Sept in the morning three long range bombers crossed the South Coast dropping bombs in Somerset, Wiltshire and Sussex, and 2 Fw190s dropped bombs and opened fire with m.g. in Kent. These raids caused considerable damage to a factory, a military reception centre, a boy's school and a colliery'. The PRO also holds files on the interception of Luftwaffe radio reports which may indicate which units were operating, but I am not sure which files these would be held on possibly around AIR22/500,
Brian Bines