In addition to his overall structural problem of how to support the weight of the lantern tower, a s I see it, the Master Carpenter is trying to solve several subsidiary problems, one of which is to be seen in this detail : There are no less than 13 joists, major and minor, which must come together at a single point ("A").

This detail of one of the eight primary joint confluences at the "floor" (as Hewett terms it --the wooden vaults are below, the lantern tower above) level of the Ely Octagon illuminates part of the complexity of design which was necessary to construct this extraordinary structure.
Note that all of the secondary and tertiary beams ("joists" as it were, since this may be called a "floor") conververge, ultimately, upon the single vertical beam/"pilaster," "A."
That is, all of the weight/stress of all of these elements (as well as those of the wall beams, "f") was carried to the ground via the vertical beam "A" except for that which was carried by the wooden ribs below. If this stress was essentially carried by the beams/joists which we see here, then an examination of the type of joints used should suffice to demonstrate this. The question then becomes : What is the nature of these joints?
Since, in any wooden joint, grain is an essential element, I've added some lines to emphesize the direction of the grain in these beams, together with shading to clarify the upper surfaces.