Edit the following files (with Notepad):

cs757_g_nose.fx
cs757_g_taxi.fx
cs757_g_turn.fx
cs757_g_wing1.fx
cs757_g_wing2.fx

They are found in the P3Dv4\Effects folder.

If you you click on Regular, or Low, in the ACE, and accept the changes, you will change them back unless you modify the original files (not recommended) found in P3Dv4\Captain_Sim\757-III\ace\reflection\100 and P3Dv4\Captain_Sim\757-III\ace\reflection\070

Back up the original files before making any changes! ;)

Replace P3Dv4 with FSX, FSX-SE, or P3Dv3 for the 32bit version.