I had 12% SDI and didn't get a 3rd PS for the day. I believe this is the second day in a row.

The rules changed in round 6:

SDI increases the maximum number of planned strikes per day. One additional planned strike is guaranteed for every 15% of SDI and another PS strike is randomly awarded based on the remainder of the tech. For example, 20% SDI grants 1 additional planned strike with a 33% chance of another planned strike. The maximum number of PS per day is refreshed when bonus acres are awarded.

I've gotten an extra PS every day I've been over 11%. Are you saying I've been abnormally lucky in hitting that extra PS chance?

Yes.