FULL TANK....LONGER STARTING??UMMMM

[vw754]

Im not sure but im testing yet but,i think ive notice when my tank is full to the brim,car takes a few seconds longer to start,if ive used around ...say 20 litres,its starts as soon as i turn the key....any idea's?

AUDI A4 TDI 130BHP 2001 (B6) AWX ENGINE