Because I planned the model, so if I may, I'll answer.
The tabs are designed to give lateral support to the lower parts of the fuselage, so that assembling them and connecting them to the bottom of the body will be easier and more convenient.
YOAV
The original tabs(no' M) look like this.
And here, with the half-formers between them.
I will give Joseph the honor to show how the lower parts look in their final form.