* fix can't load Slingload_01_Base_F
20ft containers (`Land_Cargo20_military_green_F`) can be loaded but all children from `Slingload_01_Base_F` which share the same real size of a 20ft container can't be loaded (ex: `B_Slingload_01_Ammo_F`)
* add a comment next to the changed line
add a comment next to the changed line indicating why it has to be like that (the point of this PR) for future source reference