Maximal chains of isomorphic subgraphs of countable ultrahomogeneous graphs

For a countable ultrahomogeneous graph G=〈G,ρ〉$\mathbb{G}=〈G,\rho 〉$ let P(G)$\mathbb{P}(\mathbb{G})$ denote the collection of sets A⊂G$A\subset G$ such that 〈A,ρ∩[A]²〉≅G$〈A,\rho \cap {[A]}^2〉\cong \mathbb{G}$. The order types of maximal chains in the poset 〈P(G)∪{∅},⊂〉$〈\mathbb{P}(\mathbb{G})\cup \{\varnothing \},\subset 〉$ are characterized as: