What Triggers the Addition of New Balls in 'Relentless' Mode?

Question

The description for Magnetic Billiards Relentless game mode reads:

Balls from the tube will be gradually added to the table.

How long will you last?

However, I'm not entirely sure what actually triggers the addition of new balls. This is annoying because the bonus for completely clearing the table is very high, and I can't reliably do this without understanding when new balls will appear.

It seems to be quasi-random, usually waiting until there are only one or two single balls left not in clusters, but this isn't always the case, as you can see from the screenshot below.

What triggers this?

Answer 1

It's not random. The process of adding balls to the table is triggered when the number balls remaining falls below a certain threshold (25% I think) and continues for several shots until the the table contains the original number of balls.

If you clear the table quite quickly it's entirely possible to clear it completely at which point the table will be refilled in one go.

The idea was to create some sort of ebb & flow with the table getting quite empty at times an very full at other times. Replacing the balls constantly proved frustrating and far less interesting to play.