This mod claims Simpler Platform Drag makes "all platforms with the same shape have the same speed". I am interested to know the meaning of this claim.

I might not be exactly right. That's just how I understood it at that time. I'll look at the equation in the code again...

It takes a square root of weight to determine the "effective" width of a platform. The width drag is linearly proportional in stock, as is also thrust, because it correlates to the maximum number of engines that could be placed on the ship. Because of that the stock top speed relies only on the quality of engines. So all ships with dimensions X * Y have their thrust proportional to X and their weight proportional to X * Y. If X=Y taking the square root of weight just returns X. So its top speed remains the same regardless of the ship size. If X>Y then √W<X, top speed increases. But the increase is only proportional to the difference between X and Y. Or likely to the square root of it... Lets just make an image: https://i.imgur.com/lM3YfCI.png

Not exactly proper math on my part in the picture, but yeah, top speed with this equation only depends on the shape so all similar in shape ships should reach the same speed.

I mean yeah, longer ships become slower, my mod also works like that. The difference is in my mod a ship with twice the width and twice the thrust keeps the same speed, and in Simpler Drag it gains (two minus square root of two) of effective thrust (so around 59% of base) and begins accelerating.