You can ctap a sticky, that's how you can kill yourself with just 2 stickies.
https://developer.valvesoftware.com/wiki/TF2/Team_Fortress_2_Mapper's_Referencethis says 1 sticky will get you a maximum of 960 units vertical. it has the right soldier ctap height so it could be accurate, you got 1028 though so who knows if its any good
Did some testing, highest I could get was 1028 units.
This map is not going to be fun