Canna small buds? I don't think so that would indeed be user error..
The only reason you're not getting the fat nugs you're looking for is canopy to light ratio & distribution.
I'm gonna repeat myself again but
You can't do more than what the lights can give you.. if you want the type of plant you shape to be full of fat chunks you need more power.
Like according to manufacturer one of those lights can yield 75 to 100gr in optimum conditions. now that 100gr if you divide the plant under it into 16 branches.. how is that going to look? that's going to be 16 branches giving you 6,25 each.. that's not going to be 16 branches with the fattest biggest buds you've ever seen as that would total to a lot more than what the light can do.
And you're probably close to what the lights can do as you say you get +-300gr from the tent, you're just getting it in loads of smaller nugs as you create a whole lot of them.