Starfleet2CE.exe
I found the variable that determines Phaser Efficiency vs Plasma. It is initially set to 0.25d. Doublechecked everything and the customizable variable works. Plasma is easily thwarted in normal SFC with 50%+ efficient Phasers vs Plasma Torps. You can starcastle if you can't phaserboat. 20% to 30% is reasonable.
I also found those peculiar Plasma Damage Brackets. You'll be able to adjust the decay rate for all the plasma types. Unfortunately many of the damage multipliers are shared with unrelated functions, so it will take time to isolate them. But the brackets for Plas-R, S, and G are easy to edit.
Modded Plasma-"R" (Plasma-R2?)
Damage after traveling nominal hexes
0-10 = 50
11-15 = 45
16-20 = 40
21-25 = 35
26-28 = 20
29-30 = 10
31 = 1
or
Modded Plasma-"R" wave (Plasma-W?)
Damage after traveling nominal hexes
0-10 = 5
11-15 = 10
16-20 = 25
21-25 = 50
26-28 = 25
29-30 = 10
31 = 5
endless mods...
Add to CE offsets.txt
63B990: 1f // Plasma-R 1st range bracket // 0.3548 ; 11/31
63B99C: 1f // Plasma-R 2nd range bracket // 0.5161 ; 16/31
63B9B0: 1f // Plasma-R 3rd range bracket // 0.6774 ; 21/31
63B9C8: 1f // Plasma-R 4th range bracket // 0.8387 ; 26/31
63B9D4: 1f // Plasma-R 5th range bracket // 0.9355 ; 29/31
63B9E4: 1f // Plasma-R 6th range bracket // 0.9677 ; 30/31
63B998: 1f // Plasma-S 1st range bracket // 0.4231 ; 11/26
63B9A8: 1f // Plasma-S 2nd range bracket // 0.6154 ; 16/26
63B9C0: 1f // Plasma-S 3rd range bracket // 0.8077 ; 21/26
63B9D0: 1f // Plasma-S 4th range bracket // 0.9231 ; 24/26
63B9E0: 1f // Plasma-S 5th range bracket // 0.9615 ; 25/26
63B9A0: 1f // Plasma-G 1st range bracket // 0.5238 ; 11/21
63B9BC: 1f // Plasma-G 2nd range bracket // 0.7619 ; 16/21
63B9CC: 1f // Plasma-G 3rd range bracket // 0.9048 ; 19/21
63B9DC: 1f // Plasma-G 4th range bracket // 0.9524 ; 20/21
The values for the brackets should increase from one to the next. Giving a 4th bracket a value less than the 3rd bracket is not going to crash the game. It is just difficult for a person to follow the flow. You can give the first bracket a value of 1.0, and the torpedo will not degrade as it travels -- same as a missile.