Sodium Phosphate Reloading

All, I have a big event at the end of August (30th). Then I have another big event coming up on September 21. I've used So Phos in the past with good success and plan to use it again for these races. The thing is, I've never used it so close together in a season.

Have any of you tried using it with only 3 weeks in between phases like this?

Are there any concerns about it losing its effectiveness because it's such a short interval in between load phases?

Thanks ahead.