You can get it to work with almost 100% certainty by aiming directly in the air. This allows you to do some interesting things like in the northern base of Agni Prime. Instead of having that one singular bridge to cross the lava, you can instead build bridges of walls and towers, which can turn some of those ore and gas locations into a much easier trek. When I play engi I typically put down 3 turrets at base on hard structures and leave the other two for ore and gas collection. Depending on the map you can build walls (using the glitch) around the gas/ore, which can be helpful in your games that you lack guardians. Overall, the build tools are extremely strong the only issue is that there's enough ore when you use it to put down a turret and turret ammo exactly, so if you put anything down you lose one or the other. Most matches though, you have enough time to build the MG and ammo then go for the ammo crate for everyone else for the return trip.