water question for brewing with oats

hi all,
just a quick question concerning a recent weissbier i brewed. i used 400g of oats in the grain bill for a 25l (6.6gal) brew and, while i usually have no trouble in hitting my targets for wort extraction, i was 2 litres light after sparging (getting 33l of wort instead of the 35l i should have got).
i don't know if someone out there has had this experience when brweing with oats but my question is this: is this due to the oats in the mash soaking up more liquid than grains would have and, if so, should i therefore mash (or sparge) with additional water in the future (from the experience here i would guess that for the oats i used, a litre of water per 200g of oats would sort this out) ???
any help would be greatly appreciated !!
cheers,
jon

I very much doubt that 400g of oats would soak up 2 liters of water on top of what you've already calculated. I think you need to look for another reason.

The difference in water absorption between flaked oats/wheat/barley and regular crushed grains is pretty negligible.  With the loading of oats you cited for a 25 liter batch, it would amount to less than 100 ml.  I'm with Roadrocket, you need to look elsewhere for you water discrepancy.