General Scale Calculation Question and 1/16th K5 dimensions

[braq]

Dear all,

could you please comment on my thoughts on how to derive true scale relations, let's take the K5s dimensions as an example:
http://en.wikipedia.org/wiki/Chevrolet_K5_Blazer

Length 184,8/4694 (inches/millimeter)
Width 79,6/2022
Wheel Base 106,5/2705

Ratio of Length/WB = 1,73

I would like to build a scaler that fits my fleet of Bruder (1/16) trucks....
Dividing the dimensions by 16
Length 293mm
WB 169mm
Width 116mm
Ratio L/WB 1,73

Looking at the Proline body (supposed to fit 1/18 losi MRC)

Length 318mm
WB 213mm
Width 112mm
Ratio L/WB 1,48

I wonder how that is supposed to work?
I can surely understand that the original data includes the bumpers whereas the proline's body is missing that, but the L/WB ratio still is "off" and the width matches almost perfectly (112mm/25.4*18=79,3inches)

Any good advice on how I make a mistake in my calculations or is the Proline body enlongating the real proportions?

Regards,

Braq