If you use the inner platform as reference, the length of all platforms would change when adding/removing tracks, making it impossible to upgrade such stations with a different amount of tracks.
Taking that into account, I think the current solution is better than the one you suggested, although it's not perfect.

So the prefect solution is to make all platforms the same length, although it result in much more calculates and doesn't reflect to reality.

I don't understand your complaint Merk, The outer platforms should just take up a larger angle of the circle. The over all shape of the station would be a trapezoid with the minor side as the inner track,and the major side as the outer track.

Use the existing system

Pros:

• No change in code needed
  
• Works well when placing the station building on the inside of the curve
  
• All stations line up evenly (cover the same angle)
  
• Existing infrastructure does not need to be changed in order to increase station width

Cons:

• Placing the station building on the outside means inside tracks added will get progressively smaller than the desired station length
  
• Must plan ahead with projected station track width and use math or guesswork to ensure the correct station length on the projected inside track

Redesign the system so that the station building can be on the outside and the added inside track will be the desired length

Pros:

• Can put station buildings on the outside of the curve
  
• No matter what the inside track will be the desired length
  
• All stations will line up evenly (cover the same angle)

Cons:

• Must change code
  
• In order to have the stations line up with each other, the existing outside stations must be lengthened
  
• This means that existing rail infrastructure must be destroyed before upgrading the station width

Redesign the system so that the station building can be on the outside and the added inside track will be the desired length, but do not change the existing rail infrastructure.

Pros:

• Can put station buildings on the outside of the curve
  
• No matter what the inside track will be the desired length
  
• Existing infrastructure does not need to be changed in order to increase station width

Cons:

• Must change code
  
• Stations will not line up with each other (will not cover the same angle)

• Solution 1 looks good but added stations get progressively smaller
  
• Solution 2 looks good but existing infrastructure must be destroyed when modifying the station in any way
  
• Solution 3 is perfectly functional but is not pleasing to the eye