It must be Ne. What an Si user perceives or takes in from the extnernal must be Ne, they just don't 'look at it' or are less 'consciously aware' of it. So the external data is absorbed via Ne, but they only pay attention to the inner, subjective sensate impressions of Ne uptake. Yay, Nay, Cray?
Edit: Sorry @Hicks , I'm not actually directing this at ya lol.. I'm more or less rambling to myself. Don't feel obligated to respond!
I bet you we are perceiving with more than Ni, Si, Ne and Se. There is on average 11 million pieces of data coming at us, while we process about 40 of it. ha ha ha. A nice slice of humble pie.