In the quantum Hall regime, the longitudinal resistivity ρxx plotted as a density-magnetic-field (n2D − B) diagram displays ringlike structures due to the crossings of two sets of spin split Landau levels from different subbands [e.g., Zhang et al., Phys. Rev. Lett. 95, 216801 (2005)]. For tilted magnetic fields, some of these ringlike structures "shrink" as the tilt angle is increased and fully collapse at θc ≈ 6 • . Here we theoretically investigate the topology of these structures via a non-interacting model for the 2DEG. We account for the inter Landau-level coupling induced by the tilted magnetic field via perturbation theory. This coupling results in anti-crossings of Landau levels with parallel spins. With the new energy spectrum, we calculate the corresponding n2D − B diagram of the density of states (DOS) near the Fermi level. We argue that the DOS displays the same topology as ρxx in the n2D − B diagram. For the ring with filling factor ν = 4, we find that the anti-crossings make it shrink for increasing tilt angles and collapse at a large enough angle. Using effective parameters to fit the θ = 0 • data, we find a collapsing angle θc ≈ 3.6 • . Despite this factor-of-two discrepancy with the experimental data, our model captures the essential mechanism underlying the ring collapse.