Options Set To Increase Price By % Not Calculating Properly

Hello

I have a website that is using % increases on some options. But the correct totals are not being reached.

For example, this shed costs £910.78 in size 12x8.

This is worked out from a base price of £394.66 for the smallest option with a modifier for £ set at £516.12 for the 12x8 size.

[url=https://postimg.cc/n9ZMYZdn]base-price.jpg[/url]

[url=https://postimg.cc/2VShPFwr]size-price-increase.jpg[/url]

This brings the price to £910.78.

The next option is Heavy Duty and the modifier is a % of +25%. This brings the price, incorrectly to £1009,45.

[url=https://postimg.cc/jLndwDqy]wrong-price.jpg[/url]

The actual price should be £1,138.47

Why are the prices not being worked out correctly?

Ok so whats its actually doing is only putting the +25% on the base price - not the base price + first option (size).

How do I get the options to work out a price from the base price + any previously set option?

Like this

Base Price - £394.66

First Option - Size 12x8 £516.12 + Base Price £394.66 = £910.78

Second Option - Increase £910.78 by 25% (not just the base price of £394.66)

etc

Anyone!?

We can help to solve this problem for you. Please feel free to contact us here.

I'm not looking for pay for modifications. This is a pretty standard CS-Cart system, I just want to know why it's not working and how to fix it. Any ideas?

In this case post message to the bug tracker. But most possibly "it is designed so"

Been like this for years, you need someone to dev it for you

If devs want to inbox me with a quote please feel free. Need this fixing.