What strategy assessment did you use initially?
I don’t know that there is an absolute formula, but I have heard that if 80% of your students show a need, that’s a good whole class strategy lesson. Sometimes you will work on the same strategy in whole and small group, but sometimes it will be a different one, depending on the needs of the students. For example, you might introduce check for understanding as a whole group strategy but emphasize chunk letters and sounds as a small group focus.

I go by the 80% rule, too. If most of them need a skill, I teach it whole-group. I think it’s ok to teach almost all reading strategies whole-group (except for accuracy in the older grades), and then just differentiate during small groups and conferring time. I think all students need to be reminded of certain strategies from time-to-time. There are so many different strategies, and good readers use them all, when appropriate.