That park is simply atrocious for hitters. But, it wasn't just a park issue for Giles. His home/away splits:
Home: .287/.376/.488; 45 R, 41 RBI; .180 ISO
Away: .282/.372/.462 ; 52 R, 53 RBI; .201 ISO
The R/RBI stats are more indicative of his teammates, I think, who may have had an easier time getting on base and driving him home while out of Petco. Giles, however, had a worse OBP and SLG at Petco.
Check out his 2004 splits
again his 2003 splits
He absolutely fell apart against lefties, last year (SLG went from .476 to .460 to .351 against lefties over the past three years). I can't find any splits about how he hit lefties at home versus away, so I'm not certain if it's a Petco issue, but I doubt it. I could compile a list of box scores at Petco and away from Petco, but that'd just be too much work...
If anybody has those splits, let me know.
[Edit: His EQBA for last year was .298, though; that ranks him 8th among MLB outfielders with 600+ PA.]
Your wisemen don't know how it feels to be thick as a brick...