Correct air filter is installed, and sitting correctly in the bottom housing?
The upper housing placed correctly on top of the air filter and all clips correctly latched?
If so, the perceived gap is fine.
If you examine the air filter, there is a rubber gasket that goes around the perimeter of the air filter. This rubber gasket makes an air tight seal so NO un-metered air or water enters. This rubber gasket is sandwiched between the upper and lower air filter housing. The clips are apply pressure onto the rubber gasket, to ensure an airtight seal. NO UN-METERED air passes through this perceived gap.
The mold used to make the upper air box lid, for whatever reason was NOT designed to have the edge go around and make the perceived "gap" disappear. Yes, from an aesthetic point, Toyota should have just made the upper lip come around so there is no "gap." But, there is no problem with the design: the lid holds the air filter in place, and the clips apply the necessary pressure against the rubber gasket for an AIR TIGHT SEAL.
If this was a true gap, there would have been TSBs, possibly recall, lawsuit, and numerous postings about this perceived gap. Also, the CEL would remain on.
There is no rubber gasket on the filter, it is all paper. Make sure your tabs on the back of the top half on either side of the intake tube are all the way into the corresponding hooks on the bottom half.