BEST PRACTICES – Scaling in to a new position

Hi Pat - I know you like to scale into new positions, with each successive entry having a smaller number of shares than the preceding entry, until you have a full position, . . . assuming of course that the Market and the Stock are BOTH working. If I remember right, the rough percentages can go like this.
1st entry  50%
2nd entry 30%
3rd entry  20% Understanding that we want to keep our entries as close as possible to the optimal buy point, and we don't want to chase a stock, I was curious to know what you use as a guideline for the (2) follow-up buy points. Thanks
Mike