You're doing the math way wrong, but whatever

Who cares if no one can see your militia/starter fit?

these modules also have a stacking penalty

They do have stacking penalties

Assuming you have lvl 5 Dampening, your profile would be something like:

50 * 0.9 * (1 - 0.85) * ( 1 - 0.85 *0.86 ) = 33.3
50 * 0.9 * (1 - 0.85) * ( 1 - 0.85 *0.86 ) * ( 1 - 0.85 * 0.56) = 30.5

Edit:
Even though the game doesn't mention it, they do. There have been numerous tests over it and I believe a Dev even confirmed it recently.

Reduces the length of the delay before shield recharge begins.

NOTE: Stacking penalties apply to this module; the effectiveness of each additional module (after the first) that alters the same attributes will be reduced.

Decreases drospuit's scan profile making it harder to detect by scanning systems.

OP raises an interesting point. If OP believes that hiding from scanners is a big deal, surely others do too. Which inversely means there are people who trust their scanners too much.

Sp GÇô (Sp*Ds) GÇô (Sp*Dm) Where:
Sp = Scan Profile,
Ds = Dampening Skill % efficacy,
and Dm = Dampener Module % efficacy.

Consequently, at lvl 2 Profile Dampening with a Basic Profile Dampener module you get:
Sp GÇô (Sp*0.04) GÇô (Sp*0.15)

I know it's not above STD.

also, you got a 28.05%, not 29.99%.

15, 15

ED: I'd suggest using the DUST514 Fitting Tool for things like this. The tool's math and stats are solid, and it gets updated fairly frequently with new discoveries about how the stat math works. (It accurately models stacking penalties on dampeners, even though they aren't mentioned as having penalties in game.)

I don't care what kind of math you do for militia suit voodoo... It's still made out of plastic and my scrambler will melt a whole through it soon as I see you.

That said, I will give you hats off on using starter fits as a tool though, they are an over looked tool for newbies. When I first joined Dust I played for about a month before I put the first SP into dropsuits. Essentially I had a bank role of about 25mil ISK and actually understood what I wanted to do in the game and figured out which corp I wanted to join. I do wish that I had chose Caldari as a race since I'm specializing in Caldari assault...would have made the bonuses on the start suits jive well.

If only scanners would not give margin of error message...

Someone pointed that out on another post and a CCP dev already said that all the electronic upgrade mods have stacking penalties.

Right now I have to say that the Gallente suits are the best. For logistics, their cpu/pg bonuses are wonderful. Their low slots are perfect also for a good tank, as shields are complete garbage right now against AR's and SAR's, which do incredible damage. The Assault suit is also amazing as it has another great fitting bonus for the pg/cpu for the Assault Rifles and hybrid weapons...

Scouts are great because of the scanning bonus. They provide the best bonuses for this current build.

So, I pull out an active scanner. These are your options.

1. Play normally. You are all marked for my squad.
2. Use dampeners. You die twice as fast to my whole team.

I like that.