  We had earlier shown that for a constant velocity jet the discrepancy between
the low speeds indicated by VLBI knot motions and the high Doppler factors
inferred from emission of TeV photons could be reconciled if ultrarelativistic
jets possessed modest opening angles. Here we evaluate the (flux-weighted)
viewing angles of the jet and the apparent speeds and Doppler factors of the
radio knots on parsec scales. The influence of the jet opening angle on these
radio knot parameters are found for the usually considered types of
relativistic nuclear jets: those with uniform bulk speeds and those where the
bulk Lorentz factor of the flow decreases with distance from the jet axis,
known as `spine--sheath' flows. For both types of jet velocity structures the
expectation value of the jet orientation angle at first falls dramatically with
increases in the (central) jet Lorentz factor, but for extremely relativistic
jets it levels off at a fraction of the opening angle. The effective values of
the apparent speeds and Doppler factors of the knots always decline
substantially with increasing jet opening angle. The rarity of highly
superluminal parsec-scale radio components in TeV blazars can be understood if
their jets are both highly relativistic and intrinsically weaker, so probably
less well collimated, than the jets in ordinary blazars.
