if i may make an attempt at an answer (and please correct me if i am wrong)...
first let me redefine your terms to make sure we are talking about the same thing. by 'reaction numbers' i assume that you mean each fib node or retrace level such as 23.6, 38.2, 50, and so on. and by 'focus number' i assume that you mean the starting low or high from which to draw the fib retracements or extensions.
if the above is true, then:
let's assume a bullish trend with a low denoted 'L' and a high denoted 'H'. furthermore, let's also assume a significant pullback within that bullish trend, that is, between L and H. this pullback gives us a new intermediate low denoted L'. and let's assume the bull trend resumes after L' to end at the same high as the larger trend mentioned before, that is, H = H'.
now, we will draw the first fib retracements from L to H. and then we will draw a second fib retracement from L' to H.
i will call a particular fib retracement level a fib node. that is, 38.2 is a fib node, and so on.
let's denote the whole first fib retracement structure of the larger move by fibLH and the secondary fib retracement structure within that larger move by fibL'H.
my understanding of confluence is this: if we have a fib node from fibLH that coincides with a fib node from fibL'H, say, for example, fibLH(38.2) comes very close to fibL'H(61.8)--and 'close' here i guess depends on the time frame (TF), but usually it will be within the following range (in terms of pips) [0, 15] on H1/H4, and wider on higher TFs--then that would be a confluence, that is, a coming together of 2 significant fib nodes drawn from 2 different fib retracement structures. sometimes, for a particular trend, you can draw more than 2 fib retracement structures.
as regards fib extension (ext) structures, the starting point will also be L (for bullish trends, H for bearish trends). if a fib ext node coincides (close enough) to a fib retrace node, then we have an agreement area.
fib ext structures are also drawn within the context of a forming AB=CD structure after the AB and BC legs are completed in order to estimate a potential end point for the CD leg.
hope i made no mistakes ;-) and that it makes sense.