  The half-infinite XXZ spin chain with a triangular boundary is considered in
the massive regime. Two integral representations of form factors of local
operators are proposed using bosonization. Sufficient conditions such that the
expressions for triangular boundary conditions coincide with those for diagonal
boundary conditions are identified. The expressions are compared with known
results upon specializations.Using the spin-reversal property which relates the
Hamiltonian with upper and lower triangular boundary conditions, new identities
between multiple integrals of infinite products are extracted.
