I have gone through the couplet 7s in the top 10000.
And I have created a couple of new spreadsheets for the 4s and 5s.
Sheet 1: blockers split between 3 letter word plurals and others. Others then split on ending letter.
Sheet 2: not blockers but no S back hook
Sheet 3: the rest
I have excluded all the 4 letter words + S from sheet 3 of the previous spreadsheet and made 2 sheets for blockers - hooks of 4s and not hooks of 4s.
I have beautifully coloured them.
Now I just have to print them off and study them...