Advanced spread on exchange rate rules

[wtzr]

Is your feature request related to a problem? Please describe.
We are dealing with a very wide range of bitcoin order amounts per invoice. To mitigate our conversion risk and give our customers the best rate possible, it would make sense for us to have a higher exchange spread for larger invoices.

Describe the solution you'd like
It would be nice to have an option, perhaps in the rate rule scripting area, where we could set an exchange spread rule based on the amount on the invoice. For example:

• if [invoice amount > 100.000] than [exchange spread = 1.2]
• if [invoice amount< 100.000] than [exchange spread = 0.8]

Describe alternatives you've considered
At this moment we have chosen to increase the spread on all invoices, but it's not entirely fair for customers that pay a smaller invoice.

[wantabit]

This would be helpful!