HoMM IV Reference Guide.

The bonus only applies to one object of the same type – stable, trough, oasis, etc.

Hmm, I'm not sure about this statement. Isn't it stable + trough + oasis, if they are visited on the same day?

By the way, I also noticed that the "Runner" boots or gloves enhance the bonus from movement modifiers. For example, the Grand Master's pathfinding bonus from a stable is not 5, but 7.5. I can't say for sure, but I think I noticed something like that.