querybypoint on tiled raster takes very long

[Erv McNally]

I have a raster split into 40 tiles.  When I use php mapscript querybypoint to get the elevation at
the point, it takes a long time (8 seconds).

->getResult(0) returns a tileindex and shpindex of the result.  That leads me to believe that the
querybypoint queries all tiles and not just the ones in the current extent.    I am also lead to
believe that querybypoint searches all tiles since there is no improvement of search speeds when I
am zoomed in.  I would think the farther I am zoomed in, the number of tiles used should be
smaller, therefore the amount of time required for a search should be less if querybypoint only
seached the tiles related to the current extent.

When the map draws, it may draw using only 4 tiles at a "zoomed in" extent.  I was hoping that
querybypoint would only query those same 4 tiles for the result.

Could someone tell me if querybypoint searches in the tiles associated with the current extent or
does it look at all tiles listed in the tile index?  If querybypoint searches all tiles, is there anyway to
query a small extent of a map, thereby reducing query times.  If it only searches the tiles
associated with the current extent, then I have tiling problems.

Thank you,

Erv