Advanced product options - the percentage extra is NOT dynamic and only works on base cost

[bingleyfencing]

Hi

I have advanced product options installed and i have got percentage based extras which are 15% but they only work on the base cost

if the user selects another variant the optional extra remains at 15% of the original base cost

I cannot work with this - can anyone recommend a way round this or advise of another app?

Our variations can raise from £400 to £5000 so 15 % is a lot of to lose out on!