I don't know what is on the XBR970, but in the XBR960 there is no such DHHP item in the MID1 group. It's DHPH. Is that what you're referring to?
Also, as I understand things it is the MID2 items DRHP, DRHS, DRVP and DRVS which are used for 480i. And it is the MID3 items VDHP, VDHS, VDVE and VDVS which are used for 480p, 720p and 1080i. These adjust image horizontal/vertical position/size within the background raster.
The background raster position/size is adjusted with the 2170D-1 items VPOS and VSIZ (for vertical position/size) and 2170D-2 items HPOS and HSIZ (for horizontal position/size).
I've not touched the MID1 settings when tuning my XBR960. Only MID2 and MID3 (depending on input and source being adjusted), working with 2170D-1 and 2170D-2.
As far as I can tell, I've done no harm by tweaking the MID2 and MID3 values as needed (with 16x9 test patterns). I've simply accomplished what my eyes see as "near perfection" geometry based on various test patterns.