i boldly predict that sales of oddyssey during the whole launch window will be a third of the sales of horizons, which were a third of the sales of the base game.Not sure what you mean by "will be 30% of horizons".
my rationale is that horizons was a huge leap from base with huge promise but still sold bad compared to the base game (which sold splendidly), and oddyssey is nowhere near such a paradigm shift nor has it as much value as horizons had. even if they had done really outstanding work on planetary tech (which i hope), i don't think that will attract the masses like the initial hype did.
also both releases are 'incomplete' and this time around frontier already has a reputation in that regard that is far from good, so this will have an additional toll on sales.
finally, it appears frontier strategy plays on foot fps being a popular genre yet fails to take into account the huge competition in that field, which simply blows oddyssey out of the water in every aspect. only a hardcore elite fan will look at oddyssey with the indulgence we have seen here on the forum, the only thing that oddyssey has really going for itself is the "elite" fandom loyalty.
of course i might be totally wrong ;-) time will tell!