An IPv4 address is four octets. Class C hosting varies the third one, so your sites land in different blocks. Class B hosting varies the second one, so your sites land under different parent ranges entirely: a wider gap, one step further to the left of the address.
Where Class B sits between C and A
The three products are the same hosting on three widths of address diversity, priced below as the monthly equivalent on a 3-year term. Class C is the entry level and the right answer for most networks: non-consecutive blocks, a distinct third octet per site, and the deepest European pool at $1.90/IP. Class B is the middle ground: you pay more per address and you accept a lower ceiling, and in exchange the difference between two of your sites moves from the third octet to the second. Class A goes one step further again, to the first octet, from $3.60/IP.
The honest version: none of this is a ranking factor on its own, and we will not pretend otherwise. What address diversity removes is a shared liability. Sites that answer on one parent range share a reputation, share the fallout when a neighbour is blocklisted, and present an obvious pattern to anyone who cares to look one octet to the left. Class B takes that pattern away without the price and the scarcity of a Class A allocation.
When the second octet is worth paying for
Three cases come up again and again. A small European network where every site points at the same audience and the same language: the tighter the theme, the more a shared parent range stands out. A client portfolio where the sites must not be traceable to one another, because the clients are competitors. And a set of linking domains where the whole point is that each one reads as an independent host rather than as one more entry in the same range. In all three the useful question is not "does this rank better" but "what does my footprint look like from outside", and the second octet is the cheapest place to widen it.