The heat shields are just that.. they are shields. They are bright and shiny to reflect the heat where it will go into the AIR around the barrel, and convect up through the top holes, drawing cool air in the bottom.
The idea is to REFLECT the heat, not allow it to absorb into the aluminum, and melt the plastic. Yes, handguards will get soft if you shoot enough full auto.
Leave the heat shields alone. They are for protecting the plastic of the handguard, and have no effect on the barrel.
A little physics for you... "a perfect absorber is a perfect radiator". This is why heat SINKS are flat black, they absorb heat and radiate it through the blackened fins better than if they were shiny and reflective.
JP makes finned aluminum heat sinks. Helpful hint, if you experiment with this, they should be BLACK, and no other color. A finned heat sink will clamp directly to the barrel, draw heat from the barrel, and radiate it (via more surface area) into the air from the fins.
JP's fins run lengthwise, which is fine for an unvented tube handguard. But for a vented handguard, the fins need to be radial (looking like a series of washers along the barrel) so the air can pass them from bottom to top.