I've handled a lot of Heyms, and I've never seen one with a palm swale! The Krieghoff does, however, have the palm swale. I think you might be thinking of the Krieghoff! As to the reason for the swale, there isn't one! It would be my first modification of the Krieghoff stock, the first of many for me.

I believe the Krieghoff rifles are worth their asking price,"IF" they fit you, they don't fit me at all, and feel a little like a fence post to me. The do shoot very well, and I have zero problem with the combi-cocking system on the K gun, but the type on the Blaser is Not to my likeing at all. There is no comparison between the Krieghoff and the HEYM. the Heym would be my pick of all that have been mentioned, with a B. Searcy a close second. The Merkels are more like the Britt guns in ballance that the Krieghoff, or Blaser, and IMO, are a better bargain for the price. The Heym is way up there for the PH no frills model, at $16.5K so is the Searcy at $14K, but Searcy is now offering a PH model again for around $10K to compete with the Krieghoff, and Merkels in price.

If I were the origenal poster here, I would try all the models, and brands mentioned, and take the one I could afford, that fit me best, because they are all good rifles, but the one mentioned
cover a wide range of prices. The only one I wouldn't buy under any circumstance is the Blaser, IMO there are some safety issues with useing a double rifle that doesn't recock it's self after shooting, and opening the rifle,for a re-loading. Besides life is just too short to hunt with an ugly rifle!