Getting into that vertical forearm position

On land, it really doesn’t seem all that hard to get my forearm reasonably vertical and reasonably far forward. I’d love to be able to do that in the water, but alas, it is so much tougher!

I visited Walnut Creek’s finest, Cousin Elwood, a few months back (thanks Cousin E!). He helped show me how that arm needs to get pointing down a lot more and a lot earlier. My elbow is high (now), a whole lot higher than before. But my forearm isn’t really much more vertical. At least not until I’ve pulled to at least my shoulder.

So here’s my question. Is this just (“just”??!!) a matter of increasing flexibility so that it doesn’t take so much strength to get into that position (e.g., because there’s no much resistance to get into it now)?