Roger, I've had similar experience with beer stored for a short time in small oak kegs. However, these kegs, including I assume yours for wine, were not charred. At most they were toasted, or possibly essentially plain wood. That meant a lot of raw oak flavor would leach into the liquors, quickly. However a charred cask means a layer of char is interposed between the liquor and the red layer that forms from the charring. This is not to say the smaller ratio of interior cask surface to liquid, as compared to what happens in a standard bourbon barrel, is not relevant. But again we have a barrier, the char layer, that dictates a certain relationship of barrel to spirit that does not operate with toasted or plain wood barrels. In such circumstances, it is important I think to ensure at least 100 proof, not just out of deference to tradition, but to ensure the proper amount of extractive from a charred barrel.