Just sharing my experience… I went through SA1 revision with DD and noted that she tried to determine the correct number of small boxes to draw at her first attempt (for example, in the above question, instead of drawing 3u and 1u as provided in this question, she wanted to determine if she should draw 6u and 2u at first go.) There was some confusion and anxiety and I told her not to “outsmart herself” and to take it slow when drawing model. Splitting of boxes (convenient no. of “u”) will come naturally with other information and analysis. This is what I try to show in my model above. We draw models to help us solve, not solve first and draw nice models…
If you face similar anxiety of such, do give some thoughts to the above and refer to some further examples below.