We present a constituent two-gluon description of the lowest-lying glueball states in pure Yang--Mills theory, calibrated against quenched lattice results. The framework incorporates an instanton-induced dynamical gluon mass, Casimir-scaled adjoint confinement, the short-distance adjoint Coulomb interaction, and instanton-induced central and tensor forces. The scalar 0++ glueball is found to be exceptionally compact, with a radius of order the instanton size, ρ∼31fm
Nearby in the stack
, consistent with lattice indications. By contrast, the tensor
2++
state remains spatially extended due to the centrifugal barrier. We also discuss the role of
S
-
D
mixing. A semiclassical analysis further supports Regge behavior for excited states, in agreement with lattice results.