Tropo is the propagation mode where the signal is never leaving the troposphere and in simple theory a right line between the transmitter antenna and the receiver antenna. The radio signal will, however, bend along the surface of the earth and depending on the meteorological situation and the power (E.R.P.) used. The distance covered will actually be much longer than free optical sight. On 6m, Tropo is a propagation mode of very little interest. People often also do the mistake to call Iono Scatter for Tropo. Distances over 600 kms are rarly worked and Tropo openings are also rare. Personally I cannot say that I ever worked more than 850 kms via Tropo and the station worked was EME capable. Record tables showing >1000 kms worked, are often (read: always) a result of a Iono Scatter QSO.
Forget Tropo on 6m if you are not in a contest (even more of interest in the Activity Contests), where these QSO's can give you some extra points.