The accuracy of VOCAP can be improved by using the now free EZNC to model the antenna you are using as best you can, and then importing the results into VOACAP.
If you want a simple rule of thumb, low angle radiation typically results in more band openings.
You can see this in a DX contest, like the upcoming CQ WW DX contest.
Stations with beams on towers will work stuff on 15 and 20 meters at night that most ordinary stations can't even hear.
If you are relying on the vertical radiation of an Inverted L, it may help to characterize ground conductivity as accurately as you can.