Don't think it would reflect more, but it would provide more shading. That is, the silver tarp, itself, would probably get hotter than the white one. Rather than the white tarp which seems to let too much light and IR pass through. The trick to this, I think, is to keep the tarp off the roof and allow some air circulation to prevent heat buildup underneath. We've had so much afternoon rain since the major brunt of summer started about a month ago that I've not been able to tinker with this.
2012 Rockwood A122S
2008 Toyota Tundra Double Cab 4X4
Former owner of a 2002 Coleman Niagara GTE