Q1: So if an opposite signal arrives, can I also close the position bringing the value of the “amount to close on reduction” equal to the maximum position account”?
A: To do this you would need to close the position manually.
Q2: if instead I want to ignore the opposite signal, I can put 0.0 in the “amount to close on reduction” field “?
A2: The minimum amount for “Amount to close on reduction” defaults to 0.01. So you would only experience a small reduction in the lot. To stop the reduction completely you would need to make “Amount for a new position” and “Maximum position amount” the same. This would, of course, stop the lot size from increasing when given a new buy signal.