So far, trophy waaagh bonus are based on "culture". This means, humans (bretonnia and empire) share the same, so does Tomb Kings and Vampires, etc.
What Im not sure is the specific bonus for small, big, and biggest waaagh. This threat is to gather that info from people who already made a succesful waaagh against those races.
Please, post below bonus waaagh trophy specifics. ( I only made a successful small attempt, but in process of a biggest waaagh agaainst Lothern as Grom the Paunch).
-(High) Elves: +20% Reserch, +30 % Ammunition, +20% Missile Damage
"It's small, filthy and noisy. H! Just like a dwarf!"