Hi, All!
First,make absolutely sure you are using "Scale fix One to One" mode (Properties [F8]->Common->Scale Fix 1:1.
The fans will not be accurate in normal mode.
An easy way to make a downward fan is to set the scale to -1.
(Fan->Parameters->Scale). Default is +1.
This applies to Gann Lines as well which I sometimes use to keep the clutter down from too many fans.
You can try other ratios once you get the hang of using the fans- .5, +2 etc. but in general 1:1 will fit 90% of the time. I like to add 1/3 ratio lines to my fans such as +/- .33,.67,1.33 etc- in some cases they work out well though they are not strict Gann ratios. There's a whole lotta space between the 1:1 fan line and its neighbor lines once a trend gets going!

PS: For some reason I really have to double-check in MT if my fans are at the correct angle. I will often put in a .75% line for example but it still shows up as a 1 degree line. Best perhaps is to anchor the "swing" dot of the fan, then grab the far dot and place it to a likely spot, then check what the scale box says- it will likely be an odd ratio since you were eyeballing- then type-in the scale you desire. This seems to "unlock" the fan or line if its not showing a true angle.
Cheers,
T