Partly that's an optical illusion. The whistle is slightly longer than the ACME and slightly shorter than the ACR. It looks lots longer than the ACME because of the two-way lanyard hole which makes it wide where the ACME has just a protrusion. It is about the same thickness as the ACME and the width is about the same as the ACR at its widest, but a bit narrower at both ends. In terms of total volume, it is probably a wee bit larger than the ACR and somewhat larger than the AMCE, but it packs in the same effective space in the PSP that they took up and fits in the space envelope we gave Fox 40 to work with, which is all I care about. It was re-designed specifically for this kit. So, it may not the smallest, depending upon how you measure, but it is reasonably compact and it does perform better than either one in my tests.