I may have something confused here. But, I have a 2nd gen myself with a 2010 Sienna LE. And, that is exactly where I have the filter. I did that as part of also putting my secondary transmission cooler that is over on the passenger side in front of the radiator.
All that was added given a cross country trip where I was towing a fairly heavy trailer relative to the tow allowances for the 2nd gen Sienna. Now, I did have the 'tow package' which essentially meant the oil cooler but I wanted an added boost to help keep the transmission cool.