OneFiftyThree, the use of the "big filter" is related to the problems VW is having with tome of their engines, specially the 1.8t. The sludge problem in the engine is caused (this is what I've read) by the sludge formation because of oil cooking due to the high temperature that turbo engines produce. Some people say this is an engineering issue of the engine. Anyway, to reduce the risk VW has issue and advice to all the customers and dealers to use only synthetic oil (burns at higher temps.) and use the bigger filter to increase oil circulation inside the engine.
The part number for the big filter is: 068 115 561 B (picture here:
http://www.hzyunhai.com/UploadFile/20077710357995.jpg)
The small filter part number is 06A 115 561B (picture:
http://www.made-in-china.com/image/2...A115-561B-.jpg)
Try to use original parts from VW.
I hope this could help you.