There are a couple of problems with that meme.
The first thing to recognise is that 'averaging down', can only be done while you are in a state of denial. Shares you have purchased at a higher price in the past are still worth what you paid, but new shares in the same company you buy today at a lower price are worth less - right? Of course not! All the shares you buy today are worth exactly the same market price as the shares you purchased earlier. Thus you can never "average down". That is an impossibility. You can only "average across" - pay the market price of a share as they trade on any particular day.
Next linking this piece of advice to 'the behaviour of professionals' is wrong. If that was what happened it would mean that all companies that go bankrupt would only have amateur shareholders on the share register. The professionals would never even enter the share register as the share price fell, and they would always sell down their existing positions as the share price sank. Obviously not true. In fact, because professionals tend to deal in larger numbers of shares it is more often than not their own behaviour that influences the share price direction. Not the other way around. I am sure that professionals would much prefer to sell out of their positions in a rising market. But because they hold substantial stock positions, they can't.
This behaviour is mirrored as the market rises. The reason why institutions must pay higher and higher prices if the want to accumulate a stake quickly is more often than not market liquidity. I am sure they would love to pay less for their shares ('average down' - sic). But market liquidity means that this is not possible.
Bringing this back to Ryman, I don't know what a good entry price would be. I know it is linked to the great 'kiwi property ponzi' game'. But that is a game I have always been too shy to play (to my great cost I guess, at least so far). So I will end this post with my own investment meme.
"If you don't know under what circumstances you would leave a particular investment table, then don't take a seat at the table in the first place!"
SNOOPY