Maxed trims is due to how piggies increase fuel volume. This is done by biasing (reducing) the rail pressure signal to the DME and thus DME increases pressure to meet target. This in turn gives a risk of DME recognizing HPFP issue not being able to meet pressure target. The tuning has to be below this threshold but also meet power desires of the consumer. Cold weather and AT can make the situation worse. But it does work well and is consistent when you're within the limits.
Hardware and BMW tuning can also play a role. If rail pressure is different due to these factors then the bias has an altered effect because it is a set voltage, but fuel volume percentage increase is based on actual pressure. So DME with lower pressure target for example will have greater volume increase with X bias.
You do have parameters to alter to change the end result like boost curve, E%, OL table/global.
I use Cobb with Procede and works very well.