[TowerTalk] 43 foot Vertical claim

[VO1HP]

"The DX Engineering THUNDERBOLT™ MBVA-1UP is a rugged 43 foot, high performance 160-10 meter vertical multi-band ..............this antenna is very durable, attractive, and is an optimized height of only 43 feet!"

This above line appears on a page of the DX Eng. web site for a multiband 160-10 vertical

http://www.dxengineering.com/Parts.asp?ID=3210&PLID=275&SecID=113&DeptID=22&PartNo=DXE%2DMBVA%2D1UP

Can someone tell how 43ft can be claimed as an  optimized height on 160M?

I see ads from MFJ as well for 43 ft vertical.

73 Frank VO1HP