The first time the RAF used Window operationally was on the Gomorrah raid on Hamburg.
Instruments Of Darkness by Alfred Price has this to say."The aircraft's bomb-aimers crawled back into the rear of the fuselage where the Window bundles were waiting stacked around the flare chute".
In 1944 during the Taxable spoof in support of the D-Day invasion where they had to drop 1 bundle every 5 seconds, a 617 Sqd crewman said "Our Lancaster was packed full of Window from nose to tail. if we were forced down in the sea there would be little chance of our geting out before the the aircraft sank".
On that operation the only place to carry the majority of the those bundles would be in the rear fuselage, so it would be logical to have the chute in the rear and not in the nose.